diff options
Diffstat (limited to 'old/1225.txt')
| -rw-r--r-- | old/1225.txt | 4397 |
1 files changed, 4397 insertions, 0 deletions
diff --git a/old/1225.txt b/old/1225.txt new file mode 100644 index 0000000..8a6cea9 --- /dev/null +++ b/old/1225.txt @@ -0,0 +1,4397 @@ +The Project Gutenberg EBook of Faraday As A Discoverer, by John Tyndall + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Faraday As A Discoverer + +Author: John Tyndall + +Posting Date: August 20, 2008 [EBook #1225] +Release Date: March, 1998 + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK FARADAY AS A DISCOVERER *** + + + + +Produced by An Anonymous Volunteer + + + + + +FARADAY AS A DISCOVERER + +by John Tyndall + + + + +Contents. + + Preface. + + Chapter 1. + Parentage: introduction to the royal institution: + earliest experiments: first royal society paper: marriage. + + Chapter 2. + Early researches: magnetic rotations: liquefaction of gases: + heavy glass: Charles Anderson: contributions to physics. + + Chapter 3. + Discovery of Magneto-electricity: Explanation of Argo's magnetism + of rotation: Terrestrial magneto-electric induction: + The extra current. + + Chapter 4. + Points of Character. + + Chapter 5. + Identity of electricities; first researches on electro-chemistry. + + Chapter 6. + Laws of electro-chemical decomposition. + + Chapter 7. + Origin of power in the voltaic pile. + + Chapter 8. + Researches on frictional electricity: induction: conduction: + specific inductive capacity: theory of contiguous particles. + + Chapter 9. + Rest needed--visit to Switzerland. + + Chapter 10. + Magnetization of light. + + Chapter 11. + Discovery of diamagnetism--researches on magne-crystallic action. + + Chapter 12. + Magnetism of flame and gases--atmospheric magnetism. + + Chapter 13. + Speculations: nature of matter: lines of force. + + Chapter 14. + Unity and convertibility of natural forces: theory of the + electric current. + + Chapter 15. + Summary. + + Chapter 16. + Illustrations of Character. + + + + +Preface to the fifth edition. + +Daily and weekly, from all parts of the world, I receive publications +bearing upon the practical applications of electricity. This great +movement, the ultimate outcome of which is not to be foreseen, had its +origin in the discoveries made by Michael Faraday, sixty-two years ago. +From these discoveries have sprung applications of the telephone order, +together with various forms of the electric telegraph. From them have +sprung the extraordinary advances made in electrical illumination. +Faraday could have had but an imperfect notion of the expansions of +which his discoveries were capable. Still he had a vivid and strong +imagination, and I do not doubt that he saw possibilities which did not +disclose themselves to the general scientific mind. He knew that his +discoveries had their practical side, but he steadfastly resisted +the seductions of this side, applying himself to the development of +principles; being well aware that the practical question would receive +due development hereafter. + +During my sojourn in Switzerland this year, I read through the proofs of +this new edition, and by my reading was confirmed in the conviction that +the book ought not to be suffered to go out of print. The memoir was +written under great pressure, but I am not ashamed of it as it stands. +Glimpses of Faraday's character and gleams of his discoveries are there +to be found which will be of interest to humanity to the end of time. + +John Tyndall. Hind Head, December, 1893. + + + +[Note.--It was, I believe, my husband's intention to substitute +this Preface, written a few days before his death, for all former +Prefaces. As, however, he had not the opportunity of revising the old +prefatory pages himself, they have been allowed to remain just as they +stood in the last edition. + +Louisa C. Tyndall.] + + + + +Preface to the fourth edition. + +When consulted a short time ago as to the republication of 'Faraday as a +Discoverer,' it seemed to me that the labours, and points of character, +of so great a worker and so good a man should not be allowed to vanish +from the public eye. I therefore willingly fell in with the proposal of +my Publishers to issue a new edition of the little book. + +Royal Institution, February, 1884. + + + + +Preface to the second edition. + +The experimental researches of Faraday are so voluminous, their +descriptions are so detailed, and their wealth of illustration is so +great, as to render it a heavy labour to master them. The multiplication +of proofs, necessary and interesting when the new truths had to be +established, are however less needful now when these truths have become +household words in science. I have therefore tried in the following +pages to compress the body, without injury to the spirit, of these +imperishable investigations, and to present them in a form which should +be convenient and useful to the student of the present day. + +While I write, the volumes of the Life of Faraday by Dr. Bence Jones +have reached my hands. To them the reader must refer for an account of +Faraday's private relations. A hasty glance at the work shows me that +the reverent devotion of the biographer has turned to admirable account +the materials at his command. + +The work of Dr. Bence Jones enables me to correct a statement regarding +Wollaston's and Faraday's respective relations to the discovery of +Magnetic Rotation. Wollaston's idea was to make the wire carrying a +current rotate round its own axis: an idea afterwards realised by the +celebrated Ampere. Faraday's discovery was to make the wire carrying the +current revolve round the pole of a magnet and the reverse. + +John Tyndall. Royal Institution: December, 1869. + + + + +FARADAY AS A DISCOVERER. + + + + +Chapter 1. + + Parentage: introduction to the royal institution: earliest + experiments: first royal society paper: marriage. + +It has been thought desirable to give you and the world some image +of MICHAEL FARADAY, as a scientific investigator and discoverer. The +attempt to respond to this desire has been to me a labour of difficulty, +if also a labour of love. For however well acquainted I may be with the +researches and discoveries of that great master--however numerous the +illustrations which occur to me of the loftiness of Faraday's character +and the beauty of his life--still to grasp him and his researches as a +whole; to seize upon the ideas which guided him, and connected them; to +gain entrance into that strong and active brain, and read from it the +riddle of the world--this is a work not easy of performance, and all but +impossible amid the distraction of duties of another kind. That I should +at one period or another speak to you regarding Faraday and his work is +natural, if not inevitable; but I did not expect to be called upon to +speak so soon. Still the bare suggestion that this is the fit and proper +time for speech sent me immediately to my task: from it I have returned +with such results as I could gather, and also with the wish that those +results were more worthy than they are of the greatness of my theme. + +It is not my intention to lay before you a life of Faraday in the +ordinary acceptation of the term. The duty I have to perform is to give +you some notion of what he has done in the world; dwelling incidentally +on the spirit in which his work was executed, and introducing such +personal traits as may be necessary to the completion of your picture of +the philosopher, though by no means adequate to give you a complete idea +of the man. + +The newspapers have already informed you that Michael Faraday was born +at Newington Butts, on September 22, 1791, and that he died at Hampton +Court, on August 25, 1867. Believing, as I do, in the general truth +of the doctrine of hereditary transmission--sharing the opinion of Mr. +Carlyle, that 'a really able man never proceeded from entirely stupid +parents'--I once used the privilege of my intimacy with Mr. Faraday +to ask him whether his parents showed any signs of unusual ability. He +could remember none. His father, I believe, was a great sufferer during +the latter years of his life, and this might have masked whatever +intellectual power he possessed. When thirteen years old, that is to +say in 1804, Faraday was apprenticed to a bookseller and bookbinder in +Blandford Street, Manchester Square: here he spent eight years of his +life, after which he worked as a journeyman elsewhere. + +You have also heard the account of Faraday's first contact with the +Royal Institution; that he was introduced by one of the members to Sir +Humphry Davy's last lectures, that he took notes of those lectures; +wrote them fairly out, and sent them to Davy, entreating him at the +same time to enable him to quit trade, which he detested, and to pursue +science, which he loved. Davy was helpful to the young man, and this +should never be forgotten: he at once wrote to Faraday, and afterwards, +when an opportunity occurred, made him his assistant.[1] Mr. Gassiot has +lately favoured me with the following reminiscence of this time:-- + +'Clapham Common, Surrey, + +'November 28, 1867. + +'My Dear Tyndall,--Sir H. Davy was accustomed to call on the late Mr. +Pepys, in the Poultry, on his way to the London Institution, of which +Pepys was one of the original managers; the latter told me that on one +occasion Sir H. Davy, showing him a letter, said: "Pepys, what am I +to do, here is a letter from a young man named Faraday; he has been +attending my lectures, and wants me to give him employment at the Royal +Institution--what can I do?" "Do?" replied Pepys, "put him to wash +bottles; if he is good for anything he will do it directly, if he +refuses he is good for nothing." "No, no," replied Davy; "we must try +him with something better than that." The result was, that Davy engaged +him to assist in the Laboratory at weekly wages. + +'Davy held the joint office of Professor of Chemistry and Director of +the Laboratory; he ultimately gave up the former to the late Professor +Brande, but he insisted that Faraday should be appointed Director of +the Laboratory, and, as Faraday told me, this enabled him on subsequent +occasions to hold a definite position in the Institution, in which he +was always supported by Davy. I believe he held that office to the last. + +'Believe me, my dear Tyndall, yours truly, + +'J. P. Gassiot. + + + +'Dr. Tyndall.' + +From a letter written by Faraday himself soon after his appointment as +Davy's assistant, I extract the following account of his introduction to +the Royal Institution:-- + +'London, Sept. 13, 1813. + +'As for myself, I am absent (from home) nearly day and night, except +occasional calls, and it is likely shall shortly be absent entirely, +but this (having nothing more to say, and at the request of my mother) I +will explain to you. I was formerly a bookseller and binder, but am now +turned philosopher,[2] which happened thus:--Whilst an apprentice, I, +for amusement, learnt a little chemistry and other parts of philosophy, +and felt an eager desire to proceed in that way further. After being +a journeyman for six months, under a disagreeable master, I gave up +my business, and through the interest of a Sir H. Davy, filled the +situation of chemical assistant to the Royal Institution of Great +Britain, in which office I now remain; and where I am constantly +employed in observing the works of nature, and tracing the manner in +which she directs the order and arrangement of the world. I have lately +had proposals made to me by Sir Humphry Davy to accompany him in his +travels through Europe and Asia, as philosophical assistant. If I go at +all I expect it will be in October next--about the end; and my absence +from home will perhaps be as long as three years. But as yet all is +uncertain.' + +This account is supplemented by the following letter, written by Faraday +to his friend De la Rive,[3] on the occasion of the death of Mrs. +Marcet. The letter is dated September 2, 1858:-- + +'My Dear Friend,--Your subject interested me deeply every way; for Mrs. +Marcet was a good friend to me, as she must have been to many of the +human race. I entered the shop of a bookseller and bookbinder at the age +of thirteen, in the year 1804, remained there eight years, and during +the chief part of my time bound books. Now it was in those books, in the +hours after work, that I found the beginning of my philosophy. + +There were two that especially helped me, the "Encyclopaedia +Britannica," from which I gained my first notions of electricity, and +Mrs. Marcet's "Conversation on Chemistry," which gave me my foundation +in that science. + +'Do not suppose that I was a very deep thinker, or was marked as a +precocious person. I was a very lively imaginative person, and could +believe in the "Arabian Nights" as easily as in the "Encyclopaedia." +But facts were important to me, and saved me. I could trust a fact, and +always cross-examined an assertion. So when I questioned Mrs. Marcet's +book by such little experiments as I could find means to perform, and +found it true to the facts as I could understand them, I felt that I +had got hold of an anchor in chemical knowledge, and clung fast to +it. Thence my deep veneration for Mrs. Marcet--first as one who had +conferred great personal good and pleasure on me; and then as one able +to convey the truth and principle of those boundless fields of knowledge +which concern natural things to the young, untaught, and inquiring mind. + +'You may imagine my delight when I came to know Mrs. Marcet personally; +how often I cast my thoughts backward, delighting to connect the +past and the present; how often, when sending a paper to her as a +thank-offering, I thought of my first instructress, and such like +thoughts will remain with me. + +'I have some such thoughts even as regards your own father; who was, +I may say, the first who personally at Geneva, and afterwards by +correspondence, encouraged, and by that sustained me.' + +Twelve or thirteen years ago Mr. Faraday and myself quitted the +Institution one evening together, to pay a visit to our friend Grove in +Baker Street. He took my arm at the door, and, pressing it to his +side in his warm genial way, said, 'Come, Tyndall, I will now show you +something that will interest you.' We walked northwards, passed the +house of Mr. Babbage, which drew forth a reference to the famous evening +parties once assembled there. We reached Blandford Street, and after a +little looking about he paused before a stationer's shop, and then went +in. On entering the shop, his usual animation seemed doubled; he looked +rapidly at everything it contained. To the left on entering was a door, +through which he looked down into a little room, with a window in front +facing Blandford Street. Drawing me towards him, he said eagerly, 'Look +there, Tyndall, that was my working-place. I bound books in that +little nook.' A respectable-looking woman stood behind the counter: his +conversation with me was too low to be heard by her, and he now turned +to the counter to buy some cards as an excuse for our being there. He +asked the woman her name--her predecessor's name--his predecessor's +name. 'That won't do,' he said, with good-humoured impatience; 'who was +his predecessor?' 'Mr. Riebau,' she replied, and immediately added, +as if suddenly recollecting herself, 'He, sir, was the master of Sir +Charles Faraday.' 'Nonsense!' he responded, 'there is no such person.' +Great was her delight when I told her the name of her visitor; but +she assured me that as soon as she saw him running about the shop, she +felt-though she did not know why--that it must be 'Sir Charles Faraday.' + +Faraday did, as you know, accompany Davy to Rome: he was re-engaged +by the managers of the Royal Institution on May 15, 1815. Here he made +rapid progress in chemistry, and after a time was entrusted with easy +analyses by Davy. In those days the Royal Institution published 'The +Quarterly Journal of Science,' the precursor of our own 'Proceedings.' +Faraday's first contribution to science appeared in that journal in +1816. It was an analysis of some caustic lime from Tuscany, which had +been sent to Davy by the Duchess of Montrose. Between this period and +1818 various notes and short papers were published by Faraday. In 1818 +he experimented upon 'Sounding Flames.' Professor Auguste De la Rive +had investigated those sounding flames, and had applied to them an +explanation which completely accounted for a class of sounds discovered +by himself, but did not account for those known to his predecessors. By +a few simple and conclusive experiments, Faraday proved the explanation +insufficient. It is an epoch in the life of a young man when he finds +himself correcting a person of eminence, and in Faraday's case, where +its effect was to develop a modest self-trust, such an event could not +fail to act profitably. + +From time to time between 1818 and 1820 Faraday published scientific +notes and notices of minor weight. At this time he was acquiring, not +producing; working hard for his master and storing and strengthening +his own mind. He assisted Mr. Brande in his lectures, and so quietly, +skilfully, and modestly was his work done, that Mr. Brande's vocation at +the time was pronounced 'lecturing on velvet.' In 1820 Faraday published +a chemical paper 'on two new compounds of chlorine and carbon, and on +a new compound of iodine, carbon, and hydrogen.' This paper was read +before the Royal Society on December 21, 1820, and it was the first of +his that was honoured with a place in the 'Philosophical Transactions.' + +On June 12, 1821, he married, and obtained leave to bring his young wife +into his rooms at the Royal Institution. There for forty-six years +they lived together, occupying the suite of apartments which had been +previously in the successive occupancy of Young, Davy, and Brande. At +the time of her marriage Mrs. Faraday was twenty-one years of age, he +being nearly thirty. Regarding this marriage I will at present limit +myself to quoting an entry written in Faraday's own hand in his book of +diplomas, which caught my eye while in his company some years ago. It +ran thus:-- + +'25th January, 1847. 'Amongst these records and events, I here insert +the date of one which, as a source of honour and happiness, far exceeds +all the rest. We were married on June 12, 1821. + +'M. Faraday.' + +Then follows the copy of the minutes, dated May 21, 1821, which gave him +additional rooms, and thus enabled him to bring his wife to the Royal +Institution. A feature of Faraday's character which I have often noticed +makes itself apparent in this entry. In his relations to his wife he +added chivalry to affection. + + +Footnotes to Chapter 1 + + [1] Here is Davy's recommendation of Faraday, presented to + the managers of the Royal Institution, at a meeting on the + 18th of March, 1813, Charles Hatchett, Esq., in the chair:-- + + 'Sir Humphry Davy has the honour to inform the managers that + he has found a person who is desirous to occupy the + situation in the Institution lately filled by William Payne. + His name is Michael Faraday. He is a youth of twenty-two + years of age. As far as Sir H. Davy has been able to + observe or ascertain, he appears well fitted for the + situation. His habits seem good; his disposition active and + cheerful, and his manner intelligent. He is willing to + engage himself on the same terms as given to Mr. Payne at + the time of quitting the Institution. + + 'Resolved,--That Michael Faraday be engaged to fill the + situation lately occupied by Mr. Payne, on the same terms.' + + [2] Faraday loved this word and employed it to the last; he + had an intense dislike to the modern term physicist. + + [3] To whom I am indebted for a copy of the original letter. + + + + +Chapter 2. + + Early researches: magnetic rotations: liquefaction of gases: + heavy glass: Charles Anderson: contributions to physics. + +Oersted, in 1820, discovered the action of a voltaic current on a +magnetic needle; and immediately afterwards the splendid intellect of +Ampere succeeded in showing that every magnetic phenomenon then known +might be reduced to the mutual action of electric currents. The subject +occupied all men's thoughts: and in this country Dr. Wollaston sought +to convert the deflection of the needle by the current into a permanent +rotation of the needle round the current. He also hoped to produce the +reciprocal effect of causing a current to rotate round a magnet. In +the early part of 1821, Wollaston attempted to realise this idea in +the presence of Sir Humphry Davy in the laboratory of the Royal +Institution.[1] This was well calculated to attract Faraday's attention +to the subject. He read much about it; and in the months of July, +August, and September he wrote a 'history of the progress of +electro-magnetism,' which he published in Thomson's 'Annals of +Philosophy.' Soon afterwards he took up the subject of 'Magnetic +Rotations,' and on the morning of Christmas-day, 1821, he called his +wife to witness, for the first time, the revolution of a magnetic needle +round an electric current. Incidental to the 'historic sketch,' he +repeated almost all the experiments there referred to; and these, added +to his own subsequent work, made him practical master of all that was +then known regarding the voltaic current. In 1821, he also touched +upon a subject which subsequently received his closer attention--the +vaporization of mercury at common temperatures; and immediately +afterwards conducted, in company with Mr. Stodart, experiments on the +alloys of steel. He was accustomed in after years to present to his +friends razors formed from one of the alloys then discovered. + +During Faraday's hours of liberty from other duties, he took up subjects +of inquiry for himself; and in the spring of 1823, thus self-prompted, +he began the examination of a substance which had long been regarded as +the chemical element chlorine, in a solid form, but which Sir Humphry +Davy, in 1810, had proved to be a hydrate of chlorine, that is, a +compound of chlorine and water. Faraday first analysed this hydrate, and +wrote out an account of its composition. This account was looked over +by Davy, who suggested the heating of the hydrate under pressure in a +sealed glass tube. This was done. The hydrate fused at a blood-heat, the +tube became filled with a yellow atmosphere, and was afterwards found +to contain two liquid substances. Dr. Paris happened to enter the +laboratory while Faraday was at work. Seeing the oily liquid in his +tube, he rallied the young chemist for his carelessness in employing +soiled vessels. On filing off the end of the tube, its contents exploded +and the oily matter vanished. Early next morning, Dr. Paris received the +following note:-- + +'Dear Sir,--The oil you noticed yesterday turns out to be liquid +chlorine. + +'Yours faithfully, + +'M. Faraday.'[2] + +The gas had been liquefied by its own pressure. Faraday then tried +compression with a syringe, and succeeded thus in liquefying the gas. + +To the published account of this experiment Davy added the following +note:--'In desiring Mr. Faraday to expose the hydrate of chlorine in +a closed glass tube, it occurred to me that one of three things would +happen: that decomposition of water would occur;... or that the chlorine +would separate in a fluid state.' Davy, moreover, immediately applied +the method of self-compressing atmosphere to the liquefaction of +muriatic gas. Faraday continued the experiments, and succeeded in +reducing a number of gases till then deemed permanent to the liquid +condition. In 1844 he returned to the subject, and considerably expanded +its limits. These important investigations established the fact +that gases are but the vapours of liquids possessing a very low +boiling-point, and gave a sure basis to our views of molecular +aggregation. The account of the first investigation was read before the +Royal Society on April 10, 1823, and was published, in Faraday's name, +in the 'Philosophical Transactions.' The second memoir was sent to +the Royal Society on December 19, 1844. I may add that while he was +conducting his first experiments on the liquefaction of gases, thirteen +pieces of glass were on one occasion driven by an explosion into +Faraday's eye. + +Some small notices and papers, including the observation that glass +readily changes colour in sunlight, follow here. In 1825 and 1826 +Faraday published papers in the 'Philosophical Transactions' on 'new +compounds of carbon and hydrogen,' and on 'sulphonaphthalic acid.' In +the former of these papers he announced the discovery of Benzol, which, +in the hands of modern chemists, has become the foundation of our +splendid aniline dyes. But he swerved incessantly from chemistry into +physics; and in 1826 we find him engaged in investigating the limits +of vaporization, and showing, by exceedingly strong and apparently +conclusive arguments, that even in the case of mercury such a limit +exists; much more he conceived it to be certain that our atmosphere does +not contain the vapour of the fixed constituents of the earth's crust. +This question, I may say, is likely to remain an open one. Dr. Rankine, +for example, has lately drawn attention to the odour of certain metals; +whence comes this odour, if it be not from the vapour of the metal? + +In 1825 Faraday became a member of a committee, to which Sir John +Herschel and Mr. Dollond also belonged, appointed by the Royal Society +to examine, and if possible improve, the manufacture of glass for +optical purposes. Their experiments continued till 1829, when the +account of them constituted the subject of a 'Bakerian Lecture.' This +lectureship, founded in 1774 by Henry Baker, Esq., of the Strand, +London, provides that every year a lecture shall be given before the +Royal Society, the sum of four pounds being paid to the lecturer. The +Bakerian Lecture, however, has long since passed from the region of +pay to that of honour, papers of mark only being chosen for it by +the council of the Society. Faraday's first Bakerian Lecture, 'On the +Manufacture of Glass for Optical Purposes,' was delivered at the +close of 1829. It is a most elaborate and conscientious description of +processes, precautions, and results: the details were so exact and +so minute, and the paper consequently so long, that three successive +sittings of the Royal Society were taken up by the delivery of the +lecture.[3] This glass did not turn out to be of important practical +use, but it happened afterwards to be the foundation of two of Faraday's +greatest discoveries.[4] + +The experiments here referred to were commenced at the Falcon Glass +Works, on the premises of Messrs. Green and Pellatt, but Faraday could +not conveniently attend to them there. In 1827, therefore, a furnace was +erected in the yard of the Royal Institution; and it was at this time, +and with a view of assisting him at the furnace, that Faraday engaged +Sergeant Anderson, of the Royal Artillery, the respectable, truthful, +and altogether trustworthy man whose appearance here is so fresh in our +memories. Anderson continued to be the reverential helper of Faraday and +the faithful servant of this Institution for nearly forty years.[5] + +In 1831 Faraday published a paper, 'On a peculiar class of Optical +Deceptions,' to which I believe the beautiful optical toy called the +Chromatrope owes its origin. In the same year he published a paper on +Vibrating Surfaces, in which he solved an acoustical problem which, +though of extreme simplicity when solved, appears to have baffled many +eminent men. The problem was to account for the fact that light bodies, +such as the seed of lycopodium, collected at the vibrating parts of +sounding plates, while sand ran to the nodal lines. Faraday showed that +the light bodies were entangled in the little whirlwinds formed in the +air over the places of vibration, and through which the heavier sand +was readily projected. Faraday's resources as an experimentalist were so +wonderful, and his delight in experiment was so great, that he sometimes +almost ran into excess in this direction. I have heard him say that this +paper on vibrating surfaces was too heavily laden with experiments. + + +Footnotes to Chapter 2 + + [1] The reader's attention is directed to the concluding + paragraph of the 'Preface to the Second Edition written in + December, 1869. Also to the Life of Faraday by Dr. Bence + Jones, vol. i. p. 338 et seq. + + [2] Paris: Life of Davy, p. 391. + + [3] Viz., November 19, December 3 and 10. + + [4] I make the following extract from a letter from Sir John + Herschel, written to me from Collingwood, on the 3rd of + November, 1867:--'I will take this opportunity to mention + that I believe myself to have originated the suggestion of + the employment of borate of lead for optical purposes. It + was somewhere in the year 1822, as well as I can recollect, + that I mentioned it to Sir James (then Mr.) South; and, in + consequence, the trial was made in his laboratory in + Blackman Street, by precipitating and working a large + quantity of borate of lead, and fusing it under a muffle in + a porcelain evaporating dish. A very limpid (though + slightly yellow) glass resulted, the refractive index 1.866! + (which you will find set down in my table of refractive + indices in my article "Light," Encyclopaedia Metropolitana). + It was, however, too soft for optical use as an object- + glass. This Faraday overcame, at least to a considerable + degree, by the introduction of silica.' + + [5] Regarding Anderson, Faraday writes thus in 1845:--'I + cannot resist the occasion that is thus offered to me of + mentioning the name of Mr. Anderson, who came to me as an + assistant in the glass experiments, and has remained ever + since in the laboratory of the Royal Institution. He + assisted me in all the researches into which I have entered + since that time; and to his care, steadiness, exactitude, + and faithfulness in the performance of all that has been + committed to his charge, I am much indebted.--M. F.' (Exp. + Researches, vol. iii. p. 3, footnote.) + + + + +Chapter 3. + + Discovery of Magneto-electricity: Explanation of Argo's + magnetism of rotation: Terrestrial magneto-electric + induction: The extra current. + +The work thus referred to, though sufficient of itself to secure no +mean scientific reputation, forms but the vestibule of Faraday's +achievements. He had been engaged within these walls for eighteen years. +During part of the time he had drunk in knowledge from Davy, and during +the remainder he continually exercised his capacity for independent +inquiry. In 1831 we have him at the climax of his intellectual strength, +forty years of age, stored with knowledge and full of original power. +Through reading, lecturing, and experimenting, he had become thoroughly +familiar with electrical science: he saw where light was needed and +expansion possible. The phenomena of ordinary electric induction +belonged, as it were, to the alphabet of his knowledge: he knew that +under ordinary circumstances the presence of an electrified body was +sufficient to excite, by induction, an unelectrified body. He knew that +the wire which carried an electric current was an electrified body, and +still that all attempts had failed to make it excite in other wires a +state similar to its own. + +What was the reason of this failure? Faraday never could work from the +experiments of others, however clearly described. He knew well that +from every experiment issues a kind of radiation, luminous in different +degrees to different minds, and he hardly trusted himself to reason upon +an experiment that he had not seen. In the autumn of 1831 he began to +repeat the experiments with electric currents, which, up to that time, +had produced no positive result. And here, for the sake of younger +inquirers, if not for the sake of us all, it is worth while to dwell for +a moment on a power which Faraday possessed in an extraordinary degree. +He united vast strength with perfect flexibility. His momentum was that +of a river, which combines weight and directness with the ability to +yield to the flexures of its bed. The intentness of his vision in any +direction did not apparently diminish his power of perception in other +directions; and when he attacked a subject, expecting results he had the +faculty of keeping his mind alert, so that results different from those +which he expected should not escape him through preoccupation. + +He began his experiments 'on the induction of electric currents' by +composing a helix of two insulated wires which were wound side by side +round the same wooden cylinder. One of these wires he connected with +a voltaic battery of ten cells, and the other with a sensitive +galvanometer. When connection with the battery was made, and while the +current flowed, no effect whatever was observed at the galvanometer. But +he never accepted an experimental result, until he had applied to it the +utmost power at his command. He raised his battery from 10 cells to 120 +cells, but without avail. The current flowed calmly through the battery +wire without producing, during its flow, any sensible result upon the +galvanometer. + +'During its flow,' and this was the time when an effect was +expected--but here Faraday's power of lateral vision, separating, as it +were, from the line of expectation, came into play--he noticed that a +feeble movement of the needle always occurred at the moment when he made +contact with the battery; that the needle would afterwards return to +its former position and remain quietly there unaffected by the flowing +current. At the moment, however, when the circuit was interrupted the +needle again moved, and in a direction opposed to that observed on the +completion of the circuit. + +This result, and others of a similar kind, led him to the conclusion +'that the battery current through the one wire did in reality induce a +similar current through the other; but that it continued for an instant +only, and partook more of the nature of the electric wave from a common +Leyden jar than of the current from a voltaic battery.' The momentary +currents thus generated were called induced currents, while the current +which generated them was called the inducing current. It was immediately +proved that the current generated at making the circuit was always +opposed in direction to its generator, while that developed on the +rupture of the circuit coincided in direction with the inducing current. +It appeared as if the current on its first rush through the primary wire +sought a purchase in the secondary one, and, by a kind of kick, impelled +backward through the latter an electric wave, which subsided as soon as +the primary current was fully established. + +Faraday, for a time, believed that the secondary wire, though quiescent +when the primary current had been once established, was not in its +natural condition, its return to that condition being declared by the +current observed at breaking the circuit. He called this hypothetical +state of the wire the electro-tonic state: he afterwards abandoned +this hypothesis, but seemed to return to it in later life. The term +electro-tonic is also preserved by Professor Du Bois Reymond to express +a certain electric condition of the nerves, and Professor Clerk Maxwell +has ably defined and illustrated the hypothesis in the Tenth Volume of +the 'Transactions of the Cambridge Philosophical Society.' + +The mere approach of a wire forming a closed curve to a second wire +through which a voltaic current flowed was then shown by Faraday to be +sufficient to arouse in the neutral wire an induced current, opposed +in direction to the inducing current; the withdrawal of the wire also +generated a current having the same direction as the inducing current; +those currents existed only during the time of approach or withdrawal, +and when neither the primary nor the secondary wire was in motion, +no matter how close their proximity might be, no induced current was +generated. + +Faraday has been called a purely inductive philosopher. A great deal of +nonsense is, I fear, uttered in this land of England about induction and +deduction. Some profess to befriend the one, some the other, while +the real vocation of an investigator, like Faraday, consists in the +incessant marriage of both. He was at this time full of the theory of +Ampere, and it cannot be doubted that numbers of his experiments were +executed merely to test his deductions from that theory. Starting from +the discovery of Oersted, the illustrious French philosopher had shown +that all the phenomena of magnetism then known might be reduced to the +mutual attractions and repulsions of electric currents. Magnetism had +been produced from electricity, and Faraday, who all his life long +entertained a strong belief in such reciprocal actions, now attempted to +effect the evolution of electricity from magnetism. Round a welded iron +ring he placed two distinct coils of covered wire, causing the coils to +occupy opposite halves of the ring. Connecting the ends of one of +the coils with a galvanometer, he found that the moment the ring +was magnetised, by sending a current through the other coil, the +galvanometer needle whirled round four or five times in succession. The +action, as before, was that of a pulse, which vanished immediately. +On interrupting the circuit, a whirl of the needle in the opposite +direction occurred. It was only during the time of magnetization or +demagnetization that these effects were produced. The induced currents +declared a change of condition only, and they vanished the moment the +act of magnetization or demagnetization was complete. + +The effects obtained with the welded ring were also obtained with +straight bars of iron. Whether the bars were magnetised by the electric +current, or were excited by the contact of permanent steel magnets, +induced currents were always generated during the rise, and during the +subsidence of the magnetism. The use of iron was then abandoned, and the +same effects were obtained by merely thrusting a permanent steel magnet +into a coil of wire. A rush of electricity through the coil accompanied +the insertion of the magnet; an equal rush in the opposite direction +accompanied its withdrawal. The precision with which Faraday describes +these results, and the completeness with which he defines the boundaries +of his facts, are wonderful. The magnet, for example, must not be passed +quite through the coil, but only half through; for if passed wholly +through, the needle is stopped as by a blow, and then he shows how this +blow results from a reversal of the electric wave in the helix. He next +operated with the powerful permanent magnet of the Royal Society, and +obtained with it, in an exalted degree, all the foregoing phenomena. + +And now he turned the light of these discoveries upon the darkest +physical phenomenon of that day. Arago had discovered, in 1824, that +a disk of non-magnetic metal had the power of bringing a vibrating +magnetic needle suspended over it rapidly to rest; and that on causing +the disk to rotate the magnetic needle rotated along with it. When both +were quiescent, there was not the slightest measurable attraction or +repulsion exerted between the needle and the disk; still when in motion +the disk was competent to drag after it, not only a light needle, but +a heavy magnet. The question had been probed and investigated with +admirable skill both by Arago and Ampere, and Poisson had published a +theoretic memoir on the subject; but no cause could be assigned for so +extraordinary an action. It had also been examined in this country by +two celebrated men, Mr. Babbage and Sir John Herschel; but it still +remained a mystery. Faraday always recommended the suspension of +judgment in cases of doubt. 'I have always admired,' he says, 'the +prudence and philosophical reserve shown by M. Arago in resisting the +temptation to give a theory of the effect he had discovered, so long +as he could not devise one which was perfect in its application, and in +refusing to assent to the imperfect theories of others.' Now, however, +the time for theory had come. Faraday saw mentally the rotating disk, +under the operation of the magnet, flooded with his induced currents, +and from the known laws of interaction between currents and magnets he +hoped to deduce the motion observed by Arago. That hope he realised, +showing by actual experiment that when his disk rotated currents +passed through it, their position and direction being such as must, in +accordance with the established laws of electro-magnetic action, produce +the observed rotation. + +Introducing the edge of his disk between the poles of the large +horseshoe magnet of the Royal Society, and connecting the axis and the +edge of the disk, each by a wire with a galvanometer, he obtained, when +the disk was turned round, a constant flow of electricity. The direction +of the current was determined by the direction of the motion, the +current being reversed when the rotation was reversed. He now states the +law which rules the production of currents in both disks and wires, and +in so doing uses, for the first time, a phrase which has since become +famous. When iron filings are scattered over a magnet, the particles +of iron arrange themselves in certain determinate lines called magnetic +curves. In 1831, Faraday for the first time called these curves 'lines +of magnetic force'; and he showed that to produce induced currents +neither approach to nor withdrawal from a magnetic source, or centre, or +pole, was essential, but that it was only necessary to cut appropriately +the lines of magnetic force. Faraday's first paper on Magneto-electric +Induction, which I have here endeavoured to condense, was read before +the Royal Society on the 24th of November, 1831. + +On January 12, 1832, he communicated to the Royal Society a second +paper on Terrestrial Magneto-electric Induction, which was chosen as +the Bakerian Lecture for the year. He placed a bar of iron in a coil of +wire, and lifting the bar into the direction of the dipping needle, he +excited by this action a current in the coil. On reversing the bar, +a current in the opposite direction rushed through the wire. The same +effect was produced when, on holding the helix in the line of dip, a bar +of iron was thrust into it. Here, however, the earth acted on the coil +through the intermediation of the bar of iron. He abandoned the bar and +simply set a copper plate spinning in a horizontal plane; he knew that +the earth's lines of magnetic force then crossed the plate at an angle +of about 70degrees. When the plate spun round, the lines of force were +intersected and induced currents generated, which produced their proper +effect when carried from the plate to the galvanometer. 'When the plate +was in the magnetic meridian, or in any other plane coinciding with +the magnetic dip, then its rotation produced no effect upon the +galvanometer.' + +At the suggestion of a mind fruitful in suggestions of a profound and +philosophic character--I mean that of Sir John Herschel--Mr. Barlow, of +Woolwich, had experimented with a rotating iron shell. Mr. Christie had +also performed an elaborate series of experiments on a rotating iron +disk. Both of them had found that when in rotation the body exercised +a peculiar action upon the magnetic needle, deflecting it in a manner +which was not observed during quiescence; but neither of them was aware +at the time of the agent which produced this extraordinary deflection. +They ascribed it to some change in the magnetism of the iron shell and +disk. + +But Faraday at once saw that his induced currents must come into play +here, and he immediately obtained them from an iron disk. With a hollow +brass ball, moreover, he produced the effects obtained by Mr. Barlow. +Iron was in no way necessary: the only condition of success was that +the rotating body should be of a character to admit of the formation of +currents in its substance: it must, in other words, be a conductor of +electricity. The higher the conducting power the more copious were the +currents. He now passes from his little brass globe to the globe of the +earth. He plays like a magician with the earth's magnetism. He sees the +invisible lines along which its magnetic action is exerted, and sweeping +his wand across these lines evokes this new power. Placing a simple loop +of wire round a magnetic needle he bends its upper portion to the west: +the north pole of the needle immediately swerves to the east: he bends +his loop to the east, and the north pole moves to the west. Suspending a +common bar magnet in a vertical position, he causes it to spin round its +own axis. Its pole being connected with one end of a galvanometer +wire, and its equator with the other end, electricity rushes round the +galvanometer from the rotating magnet. He remarks upon the 'singular +independence' of the magnetism and the body of the magnet which carries +it. The steel behaves as if it were isolated from its own magnetism. + +And then his thoughts suddenly widen, and he asks himself whether the +rotating earth does not generate induced currents as it turns round its +axis from west to east. In his experiment with the twirling magnet the +galvanometer wire remained at rest; one portion of the circuit was in +motion relatively to another portion. But in the case of the twirling +planet the galvanometer wire would necessarily be carried along with the +earth; there would be no relative motion. What must be the consequence? +Take the case of a telegraph wire with its two terminal plates dipped +into the earth, and suppose the wire to lie in the magnetic meridian. +The ground underneath the wire is influenced like the wire itself by the +earth's rotation; if a current from south to north be generated in the +wire, a similar current from south to north would be generated in the +earth under the wire; these currents would run against the same terminal +plate, and thus neutralise each other. + +This inference appears inevitable, but his profound vision perceived +its possible invalidity. He saw that it was at least possible that the +difference of conducting power between the earth and the wire might +give one an advantage over the other, and that thus a residual or +differential current might be obtained. He combined wires of different +materials, and caused them to act in opposition to each other, but +found the combination ineffectual. The more copious flow in the better +conductor was exactly counterbalanced by the resistance of the worse. +Still, though experiment was thus emphatic, he would clear his mind of +all discomfort by operating on the earth itself. He went to the round +lake near Kensington Palace, and stretched 480 feet of copper wire, +north and south, over the lake, causing plates soldered to the wire +at its ends to dip into the water. The copper wire was severed at the +middle, and the severed ends connected with a galvanometer. No effect +whatever was observed. But though quiescent water gave no effect, moving +water might. He therefore worked at London Bridge for three days during +the ebb and flow of the tide, but without any satisfactory result. Still +he urges, 'Theoretically it seems a necessary consequence, that where +water is flowing there electric currents should be formed. If a line +be imagined passing from Dover to Calais through the sea, and returning +through the land, beneath the water, to Dover, it traces out a circuit +of conducting matter one part of which, when the water moves up or down +the channel, is cutting the magnetic curves of the earth, whilst the +other is relatively at rest.... There is every reason to believe that +currents do run in the general direction of the circuit described, +either one way or the other, according as the passage of the waters is +up or down the channel.' This was written before the submarine cable was +thought of, and he once informed me that actual observation upon +that cable had been found to be in accordance with his theoretic +deduction.[1] + +Three years subsequent to the publication of these researches--that is +to say, on January 29, 1835--Faraday read before the Royal Society +a paper 'On the influence by induction of an electric current upon +itself.' A shock and spark of a peculiar character had been observed +by a young man named William Jenkin, who must have been a youth of some +scientific promise, but who, as Faraday once informed me, was dissuaded +by his own father from having anything to do with science. The +investigation of the fact noticed by Mr. Jenkin led Faraday to the +discovery of the extra current, or the current induced in the primary +wire itself at the moments of making and breaking contact, the phenomena +of which he described and illustrated in the beautiful and exhaustive +paper referred to. + +Seven-and-thirty years have passed since the discovery of +magneto-electricity; but, if we except the extra current, until quite +recently nothing of moment was added to the subject. Faraday entertained +the opinion that the discoverer of a great law or principle had a right +to the 'spoils'--this was his term--arising from its illustration; and +guided by the principle he had discovered, his wonderful mind, aided by +his wonderful ten fingers, overran in a single autumn this vast domain, +and hardly left behind him the shred of a fact to be gathered by his +successors. + +And here the question may arise in some minds, What is the use of +it all? The answer is, that if man's intellectual nature thirsts for +knowledge, then knowledge is useful because it satisfies this thirst. If +you demand practical ends, you must, I think, expand your definition of +the term practical, and make it include all that elevates and enlightens +the intellect, as well as all that ministers to the bodily health and +comfort of men. Still, if needed, an answer of another kind might be +given to the question 'What is its use?' As far as electricity has been +applied for medical purposes, it has been almost exclusively Faraday's +electricity. You have noticed those lines of wire which cross the +streets of London. It is Faraday's currents that speed from place to +place through these wires. Approaching the point of Dungeness, the +mariner sees an unusually brilliant light, and from the noble phares +of La Heve the same light flashes across the sea. These are Faraday's +sparks exalted by suitable machinery to sunlike splendour. At the +present moment the Board of Trade and the Brethren of the Trinity House, +as well as the Commissioners of Northern Lights, are contemplating the +introduction of the Magneto-electric Light at numerous points upon our +coasts; and future generations will be able to refer to those guiding +stars in answer to the question. What has been the practical use of the +labours of Faraday? But I would again emphatically say, that his work +needs no such justification, and that if he had allowed his vision to +be disturbed by considerations regarding the practical use of his +discoveries, those discoveries would never have been made by him. 'I +have rather,' he writes in 1831, 'been desirous of discovering new +facts and new relations dependent on magneto-electric induction, than +of exalting the force of those already obtained; being assured that the +latter would find their full development hereafter.' + +In 1817, when lecturing before a private society in London on the +element chlorine, Faraday thus expressed himself with reference to this +question of utility. 'Before leaving this subject, I will point out the +history of this substance, as an answer to those who are in the habit of +saying to every new fact. "What is its use?" Dr. Franklin says to such, +"What is the use of an infant?" The answer of the experimentalist is, +"Endeavour to make it useful." When Scheele discovered this substance, +it appeared to have no use; it was in its infancy and useless state, but +having grown up to maturity, witness its powers, and see what endeavours +to make it useful have done.' + + +Footnote to Chapter 3 + + [1] I am indebted to a friend for the following exquisite + morsel:--'A short time after the publication of Faraday's + first researches in magneto-electricity, he attended the + meeting of the British Association at Oxford, in 1832. On + this occasion he was requested by some of the authorities to + repeat the celebrated experiment of eliciting a spark from a + magnet, employing for this purpose the large magnet in the + Ashmolean Museum. To this he consented, and a large party + assembled to witness the experiments, which, I need not say, + were perfectly successful. Whilst he was repeating them a + dignitary of the University entered the room, and addressing + himself to Professor Daniell, who was standing near Faraday, + inquired what was going on. The Professor explained to him + as popularly as possible this striking result of Faraday's + great discovery. The Dean listened with attention and looked + earnestly at the brilliant spark, but a moment after he + assumed a serious countenance and shook his head; "I am + sorry for it," said he, as he walked away; in the middle of + the room he stopped for a moment and repeated, "I am sorry + for it:" then walking towards the door, when the handle was + in his hand he turned round and said, "Indeed I am sorry for + it; it is putting new arms into the hands of the + incendiary." This occurred a short time after the papers + had been filled with the doings of the hayrick burners. An + erroneous statement of what fell from the Dean's mouth was + printed at the time in one of the Oxford papers. He is there + wrongly stated to have said, "It is putting new arms into + the hands of the infidel."' + + + + +Chapter 4. + + Points of Character. + +A point highly illustrative of the character of Faraday now comes into +view. He gave an account of his discovery of Magneto-electricity in a +letter to his friend M. Hachette, of Paris, who communicated the letter +to the Academy of Sciences. The letter was translated and published; and +immediately afterwards two distinguished Italian philosophers took up +the subject, made numerous experiments, and published their results +before the complete memoirs of Faraday had met the public eye. This +evidently irritated him. He reprinted the paper of the learned Italians +in the 'Philosophical Magazine,' accompanied by sharp critical notes +from himself. He also wrote a letter dated Dec. 1, 1832, to Gay Lussac, +who was then one of the editors of the 'Annales de Chimie,' in which +he analysed the results of the Italian philosophers, pointing out their +errors, and defending himself from what he regarded as imputations on +his character. The style of this letter is unexceptionable, for Faraday +could not write otherwise than as a gentleman; but the letter shows that +had he willed it he could have hit hard. We have heard much of Faraday's +gentleness and sweetness and tenderness. It is all true, but it is very +incomplete. You cannot resolve a powerful nature into these elements, +and Faraday's character would have been less admirable than it was had +it not embraced forces and tendencies to which the silky adjectives +'gentle' and 'tender' would by no means apply. Underneath his sweetness +and gentleness was the heat of a volcano. He was a man of excitable and +fiery nature; but through high self-discipline he had converted the fire +into a central glow and motive power of life, instead of permitting it +to waste itself in useless passion. 'He that is slow to anger,' saith +the sage, 'is greater than the mighty, and he that ruleth his own spirit +than he that taketh a city.' Faraday was not slow to anger, but he +completely ruled his own spirit, and thus, though he took no cities, he +captivated all hearts. + +As already intimated, Faraday had contributed many of his minor +papers--including his first analysis of caustic lime--to the 'Quarterly +Journal of Science.' In 1832, he collected those papers and others +together in a small octavo volume, labelled them, and prefaced them +thus:-- + +'PAPERS, NOTES, NOTICES, &c., &c.,published in octavo, up to 1832. M. +Faraday.' + +'Papers of mine, published in octavo, in the "Quarterly Journal of +Science," and elsewhere, since the time that Sir H. Davy encouraged me +to write the analysis of caustic lime. + +'Some, I think (at this date), are good; others moderate; and some bad. +But I have put all into the volume, because of the utility they have +been of to me--and none more than the bad--in pointing out to me in +future, or rather, after times, the faults it became me to watch and to +avoid. + +'As I never looked over one of my papers a year after it was written +without believing both in philosophy and manner it could have been much +better done, I still hope the collection may be of great use to me. + +'M. Faraday. + +'Aug. 18, 1832.' + +'None more than the bad!' This is a bit of Faraday's innermost nature; +and as I read these words I am almost constrained to retract what I have +said regarding the fire and excitability of his character. But is he not +all the more admirable, through his ability to tone down and subdue that +fire and that excitability, so as to render himself able to write thus +as a little child? I once took the liberty of censuring the conclusion +of a letter of his to the Dean of St. Paul's. He subscribed himself +'humbly yours,' and I objected to the adverb. 'Well, but, Tyndall,' he +said, 'I am humble; and still it would be a great mistake to think that +I am not also proud.' This duality ran through his character. A democrat +in his defiance of all authority which unfairly limited his freedom of +thought, and still ready to stoop in reverence to all that was really +worthy of reverence, in the customs of the world or the characters of +men. + +And here, as well as elsewhere, may be introduced a letter which bears +upon this question of self-control, written long years subsequent to the +period at which we have now arrived. I had been at Glasgow in 1855, at +a meeting of the British Association. On a certain day, I communicated a +paper to the physical section, which was followed by a brisk discussion. +Men of great distinction took part in it, the late Dr. Whewell among the +number, and it waxed warm on both sides. I was by no means content +with this discussion; and least of all, with my own part in it. This +discontent affected me for some days, during which I wrote to +Faraday, giving him no details, but expressing, in a general way, my +dissatisfaction. I give the following extract from his reply:-- + +'Sydenham, Oct. 6, 1855. + +'My Dear Tyndall,--These great meetings, of which I think very well +altogether, advance science chiefly by bringing scientific men together +and making them to know and be friends with each other; and I am sorry +when that is not the effect in every part of their course. I know +nothing except from what you tell me, for I have not yet looked at the +reports of the proceedings; but let me, as an old man, who ought by this +time to have profited by experience, say that when I was younger I found +I often misinterpreted the intentions of people, and found they did not +mean what at the time I supposed they meant; and, further, that as a +general rule, it was better to be a little dull of apprehension where +phrases seemed to imply pique, and quick in perception when, on the +contrary, they seemed to imply kindly feeling. The real truth never +fails ultimately to appear; and opposing parties, if wrong, are sooner +convinced when replied to forbearingly, than when overwhelmed. All +I mean to say is, that it is better to be blind to the results of +partisanship, and quick to see good will. One has more happiness in +oneself in endeavouring to follow the things that make for peace. You +can hardly imagine how often I have been heated in private when opposed, +as I have thought, unjustly and superciliously, and yet I have striven, +and succeeded, I hope, in keeping down replies of the like kind. And I +know I have never lost by it. I would not say all this to you did I not +esteem you as a true philosopher and friend.[1] + +'Yours, very truly, + +'M. Faraday.' + + +Footnote to Chapter 4 + + [1] Faraday would have been rejoiced to learn that, during + its last meeting at Dundee, the British Association + illustrated in a striking manner the function which he here + describes as its principal one. In my own case, a brotherly + welcome was everywhere manifested. In fact, the differences + of really honourable and sane men are never beyond healing. + + + + +Chapter 5. + + Identity of electricities; first researches on + electro-chemistry. + +I have already once used the word 'discomfort' in reference to the +occasional state of Faraday's mind when experimenting. It was to him a +discomfort to reason upon data which admitted of doubt. He hated what he +called 'doubtful knowledge,' and ever tended either to transfer it +into the region of undoubtful knowledge, or of certain and definite +ignorance. Pretence of all kinds, whether in life or in philosophy, was +hateful to him. He wished to know the reality of our nescience as well +as of our science. 'Be one thing or the other,' he seemed to say to +an unproved hypothesis; 'come out as a solid truth, or disappear as a +convicted lie.' After making the great discovery which I have attempted +to describe, a doubt seemed to beset him as regards the identity of +electricities. 'Is it right,' he seemed to ask, 'to call this agency +which I have discovered electricity at all? Are there perfectly +conclusive grounds for believing that the electricity of the +machine, the pile, the gymnotus and torpedo, magneto-electricity and +thermo-electricity, are merely different manifestations of one and the +same agent?' To answer this question to his own satisfaction he formally +reviewed the knowledge of that day. He added to it new experiments +of his own, and finally decided in favour of the 'Identity of +Electricities.' His paper upon this subject was read before the Royal +Society on January 10 and 17, 1833. + +After he had proved to his own satisfaction the identity of +electricities, he tried to compare them quantitatively together. The +terms quantity and intensity, which Faraday constantly used, need a word +of explanation here. He might charge a single Leyden jar by twenty turns +of his machine, or he might charge a battery of ten jars by the same +number of turns. The quantity in both cases would be sensibly the same, +but the intensity of the single jar would be the greatest, for here the +electricity would be less diffused. Faraday first satisfied himself that +the needle of his galvanometer was caused to swing through the same arc +by the same quantity of machine electricity, whether it was condensed +in a small battery or diffused over a large one. Thus the electricity +developed by thirty turns of his machine produced, under very variable +conditions of battery surface, the same deflection. Hence he inferred +the possibility of comparing, as regards quantity, electricities which +differ greatly from each other in intensity. His object now is to +compare frictional with voltaic electricity. Moistening bibulous paper +with the iodide of potassium--a favourite test of his--and subjecting +it to the action of machine electricity, he decomposed the iodide, and +formed a brown spot where the iodine was liberated. Then he immersed +two wires, one of zinc, the other of platinum, each 1/13th of an inch +in diameter, to a depth of 5/8ths of an inch in acidulated water during +eight beats of his watch, or 3/20ths of a second; and found that the +needle of his galvanometer swung through the same arc, and coloured +his moistened paper to the same extent, as thirty turns of his large +electrical machine. Twenty-eight turns of the machine produced an effect +distinctly less than that produced by his two wires. Now, the quantity +of water decomposed by the wires in this experiment totally eluded +observation; it was immeasurably small; and still that amount of +decomposition involved the development of a quantity of electric force +which, if applied in a proper form, would kill a rat, and no man would +like to bear it. + +In his subsequent researches 'On the absolute Quantity of Electricity +associated with the Particles or Atoms of matter,' he endeavours to give +an idea of the amount of electrical force involved in the decomposition +of a single grain of water. He is almost afraid to mention it, for he +estimates it at 800,000 discharges of his large Leyden battery. This, if +concentrated in a single discharge, would be equal to a very great flash +of lightning; while the chemical action of a single grain of water +on four grains of zinc would yield electricity equal in quantity to a +powerful thunderstorm. Thus his mind rises from the minute to the +vast, expanding involuntarily from the smallest laboratory fact till it +embraces the largest and grandest natural phenomena.[1] + +In reality, however, he is at this time only clearing his way, and +he continues laboriously to clear it for some time afterwards. He is +digging the shaft, guided by that instinct towards the mineral lode +which was to him a rod of divination. 'Er riecht die Wahrheit,' said the +lamented Kohlrausch, an eminent German, once in my hearing:--'He smells +the truth.' His eyes are now steadily fixed on this wonderful voltaic +current, and he must learn more of its mode of transmission. + +On May 23, 1833, he read a paper before the Royal Society 'On a new +Law of Electric Conduction.' He found that, though the current passed +through water, it did not pass through ice:--why not, since they are +one and the same substance? Some years subsequently he answered this +question by saying that the liquid condition enables the molecule +of water to turn round so as to place itself in the proper line of +polarization, while the rigidity of the solid condition prevents this +arrangement. This polar arrangement must precede decomposition, and +decomposition is an accompaniment of conduction. He then passed on to +other substances; to oxides and chlorides, and iodides, and salts, and +sulphurets, and found them all insulators when solid, and conductors +when fused. In all cases, moreover, except one--and this exception he +thought might be apparent only--he found the passage of the current +across the fused compound to be accompanied by its decomposition. Is +then the act of decomposition essential to the act of conduction in +these bodies? Even recently this question was warmly contested. Faraday +was very cautious latterly in expressing himself upon this subject; +but as a matter of fact he held that an infinitesimal quantity of +electricity might pass through a compound liquid without producing its +decomposition. De la Rive, who has been a great worker on the chemical +phenomena of the pile, is very emphatic on the other side. Experiment, +according to him and others, establishes in the most conclusive manner +that no trace of electricity can pass through a liquid compound without +producing its equivalent decomposition.[2] + +Faraday has now got fairly entangled amid the chemical phenomena of the +pile, and here his previous training under Davy must have been of the +most important service to him. Why, he asks, should decomposition thus +take place?--what force is it that wrenches the locked constituents +of these compounds asunder? On the 20th of June, 1833, he read a paper +before the Royal Society 'On Electro-chemical Decomposition,' in which +he seeks to answer these questions. The notion had been entertained +that the poles, as they are called, of the decomposing cell, or in other +words the surfaces by which the current enters and quits the liquid, +exercised electric attractions upon the constituents of the liquid and +tore them asunder. Faraday combats this notion with extreme vigour. +Litmus reveals, as you know, the action of an acid by turning red, +turmeric reveals the action of an alkali by turning brown. Sulphate of +soda, you know, is a salt compounded of the alkali soda and sulphuric +acid. The voltaic current passing through a solution of this salt +so decomposes it, that sulphuric acid appears at one pole of the +decomposing cell and alkali at the other. Faraday steeped a piece of +litmus paper and a piece of turmeric paper in a solution of sulphate of +soda: placing each of them upon a separate plate of glass, he connected +them together by means of a string moistened with the same solution. +He then attached one of them to the positive conductor of an electric +machine, and the other to the gas-pipes of this building. These he +called his 'discharging train.' On turning the machine the electricity +passed from paper to paper through the string, which might be varied in +length from a few inches to seventy feet without changing the result. +The first paper was reddened, declaring the presence of sulphuric acid; +the second was browned, declaring the presence of the alkali soda. The +dissolved salt, therefore, arranged in this fashion, was decomposed by +the machine, exactly as it would have been by the voltaic current. +When instead of using the positive conductor he used the negative, +the positions of the acid and alkali were reversed. Thus he satisfied +himself that chemical decomposition by the machine is obedient to the +laws which rule decomposition by the pile. + +And now he gradually abolishes those so-called poles, to the attraction +of which electric decomposition had been ascribed. He connected a piece +of turmeric paper moistened with the sulphate of soda with the positive +conductor of his machine; then he placed a metallic point in connection +with his discharging train opposite the moist paper, so that the +electricity should discharge through the air towards the point. The +turning of the machine caused the corners of the piece of turmeric paper +opposite to the point to turn brown, thus declaring the presence of +alkali. He changed the turmeric for litmus paper, and placed it, not +in connection with his conductor, but with his discharging train, a +metallic point connected with the conductor being fixed at a couple of +inches from the paper; on turning the machine, acid was liberated at +the edges and corners of the litmus. He then placed a series of pointed +pieces of paper, each separate piece being composed of two halves, +one of litmus and the other of turmeric paper, and all moistened with +sulphate of soda, in the line of the current from the machine. The +pieces of paper were separated from each other by spaces of air. The +machine was turned; and it was always found that at the point where the +electricity entered the paper, litmus was reddened, and at the point +where it quitted the paper, turmeric was browned. 'Here,' he urges, +'the poles are entirely abandoned, but we have still electrochemical +decomposition.' It is evident to him that instead of being attracted by +the poles, the bodies separated are ejected by the current. The effects +thus obtained with poles of air he also succeeded in obtaining with +poles of water. The advance in Faraday's own ideas made at this time is +indicated by the word 'ejected.' He afterwards reiterates this view: +the evolved substances are expelled from the decomposing body, and 'not +drawn out by an attraction. + +Having abolished this idea of polar attraction, he proceeds to enunciate +and develop a theory of his own. He refers to Davy's celebrated Bakerian +Lecture, given in 1806, which he says 'is almost entirely occupied in +the consideration of electrochemical decompositions.' The facts recorded +in that lecture Faraday regards as of the utmost value. But 'the mode +of action by which the effects take place is stated very generally; +so generally, indeed, that probably a dozen precise schemes of +electrochemical action might be drawn up, differing essentially from +each other, yet all agreeing with the statement there given.' + +It appears to me that these words might with justice be applied to +Faraday's own researches at this time. They furnish us with results of +permanent value; but little help can be found in the theory advanced +to account for them. It would, perhaps, be more correct to say that +the theory itself is hardly presentable in any tangible form to the +intellect. Faraday looks, and rightly looks, into the heart of the +decomposing body itself; he sees, and rightly sees, active within it +the forces which produce the decomposition, and he rejects, and rightly +rejects, the notion of external attraction; but beyond the hypothesis of +decompositions and recompositions, enunciated and developed by Grothuss +and Davy, he does not, I think, help us to any definite conception as +to how the force reaches the decomposing mass and acts within it. Nor, +indeed, can this be done, until we know the true physical process which +underlies what we call an electric current. + +Faraday conceives of that current as 'an axis of power having contrary +forces exactly equal in amount in opposite directions'; but this +definition, though much quoted and circulated, teaches us nothing +regarding the current. An 'axis' here can only mean a direction; and +what we want to be able to conceive of is, not the axis along which the +power acts, but the nature and mode of action of the power itself. He +objects to the vagueness of De la Rive; but the fact is, that both +he and De la Rive labour under the same difficulty. Neither wishes +to commit himself to the notion of a current compounded of two +electricities flowing in two opposite directions: but the time had +not come, nor is it yet come, for the displacement of this provisional +fiction by the true mechanical conception. Still, however indistinct the +theoretic notions of Faraday at this time may be, the facts which are +rising before him and around him are leading him gradually, but surely, +to results of incalculable importance in relation to the philosophy of +the voltaic pile. + +He had always some great object of research in view, but in the pursuit +of it he frequently alighted on facts of collateral interest, to examine +which he sometimes turned aside from his direct course. Thus we find the +series of his researches on electrochemical decomposition interrupted +by an inquiry into 'the power of metals and other solids, to induce the +combination of gaseous bodies.' This inquiry, which was received by the +Royal Society on Nov. 30, 1833, though not so important as those +which precede and follow it, illustrates throughout his strength as an +experimenter. The power of spongy platinum to cause the combination of +oxygen and hydrogen had been discovered by Dobereiner in 1823, and had +been applied by him in the construction of his well-known philosophic +lamp. It was shown subsequently by Dulong and Thenard that even a +platinum wire, when perfectly cleansed, may be raised to incandescence +by its action on a jet of cold hydrogen. + +In his experiments on the decomposition of water, Faraday found that +the positive platinum plate of the decomposing cell possessed in +an extraordinary degree the power of causing oxygen and hydrogen to +combine. He traced the cause of this to the perfect cleanness of +the positive plate. Against it was liberated oxygen, which, with the +powerful affinity of the 'nascent state,' swept away all impurity from +the surface against which it was liberated. The bubbles of gas liberated +on one of the platinum plates or wires of a decomposing cell are always +much smaller, and they rise in much more rapid succession than those +from the other. Knowing that oxygen is sixteen times heavier than +hydrogen, I have more than once concluded, and, I fear, led others +into the error of concluding, that the smaller and more quickly rising +bubbles must belong to the lighter gas. The thing appeared so obvious +that I did not give myself the trouble of looking at the battery, which +would at once have told me the nature of the gas. But Faraday would +never have been satisfied with a deduction if he could have reduced it +to a fact. And he has taught me that the fact here is the direct reverse +of what I supposed it to be. The small bubbles are oxygen, and their +smallness is due to the perfect cleanness of the surface on which they +are liberated. The hydrogen adhering to the other electrode swells +into large bubbles, which rise in much slower succession; but when the +current is reversed, the hydrogen is liberated upon the cleansed wire, +and then its bubbles also become small. + +Footnotes to Chapter 5 + + [1] Buff finds the quantity of electricity associated with + one milligramme of hydrogen in water to be equal to 45,480 + charges of a Leyden jar, with a height of 480 millimetres, + and a diameter of 160 millimetres. Weber and Kohlrausch + have calculated that, if the quantity of electricity + associated with one milligramme of hydrogen in water were + diffused over a cloud at a height of 1000 metres above the + earth, it would exert upon an equal quantity of the opposite + electricity at the earth's surface an attractive force of + 2,268,000 kilogrammes. (Electrolytische Maasbestimmungen, + 1856, p. 262.) + + [2] Faraday, sa Vie et ses Travaux, p. 20. + + + + +Chapter 6. + + Laws of electro-chemical decomposition. + +In our conceptions and reasonings regarding the forces of nature, +we perpetually make use of symbols which, when they possess a high +representative value, we dignify with the name of theories. Thus, +prompted by certain analogies, we ascribe electrical phenomena to the +action of a peculiar fluid, sometimes flowing, sometimes at rest. Such +conceptions have their advantages and their disadvantages; they afford +peaceful lodging to the intellect for a time, but they also circumscribe +it, and by-and-by, when the mind has grown too large for its lodging, it +often finds difficulty in breaking down the walls of what has become its +prison instead of its home.[1] + +No man ever felt this tyranny of symbols more deeply than Faraday, and +no man was ever more assiduous than he to liberate himself from them, +and the terms which suggested them. Calling Dr. Whewell to his aid +in 1833, he endeavoured to displace by others all terms tainted by +a foregone conclusion. His paper on Electro-chemical Decomposition, +received by the Royal Society on January 9, 1834, opens with the +proposal of a new terminology. He would avoid the word 'current' if he +could.[2] He does abandon the word 'poles' as applied to the ends of +a decomposing cell, because it suggests the idea of attraction, +substituting for it the perfectly natural term Electrodes. He applied +the term Electrolyte to every substance which can be decomposed by the +current, and the act of decomposition he called Electrolysis. All these +terms have become current in science. He called the positive electrode +the Anode, and the negative one the Cathode, but these terms, though +frequently used, have not enjoyed the same currency as the others. The +terms Anion and Cation, which he applied to the constituents of the +decomposed electrolyte, and the term Ion, which included both anions and +cations, are still less frequently employed. + +Faraday now passes from terminology to research; he sees the necessity +of quantitative determinations, and seeks to supply himself with a +measure of voltaic electricity. This he finds in the quantity of water +decomposed by the current. He tests this measure in all possible ways, +to assure himself that no error can arise from its employment. He +places in the course of one and the same current a series of cells with +electrodes of different sizes, some of them plates of platinum, others +merely platinum wires, and collects the gas liberated on each distinct +pair of electrodes. He finds the quantity of gas to be the same for all. +Thus he concludes that when the same quantity of electricity is caused +to pass through a series of cells containing acidulated water, the +electro-chemical action is independent of the size of the electrodes.[3] +He next proves that variations in intensity do not interfere with this +equality of action. Whether his battery is charged with strong acid +or with weak; whether it consists of five pairs or of fifty pairs; in +short, whatever be its source, when the same current is sent through his +series of cells the same amount of decomposition takes place in all. He +next assures himself that the strength or weakness of his dilute acid +does not interfere with this law. Sending the same current through +a series of cells containing mixtures of sulphuric acid and water of +different strengths, he finds, however the proportion of acid to water +might vary, the same amount of gas to be collected in all the cells. +A crowd of facts of this character forced upon Faraday's mind the +conclusion that the amount of electro-chemical decomposition depends, +not upon the size of the electrodes, not upon the intensity of the +current, not upon the strength of the solution, but solely upon the +quantity of electricity which passes through the cell. The quantity +of electricity he concludes is proportional to the amount of chemical +action. On this law Faraday based the construction of his celebrated +Voltameter, or Measure of Voltaic electricity. + +But before he can apply this measure he must clear his ground of +numerous possible sources of error. The decomposition of his acidulated +water is certainly a direct result of the current; but as the varied and +important researches of MM. Becquerel, De la Rive, and others had shown, +there are also secondary actions which may materially interfere with and +complicate the pure action of the current. These actions may occur in +two ways: either the liberated ion may seize upon the electrode against +which it is set free, forming a chemical compound with that electrode; +or it may seize upon the substance of the electrolyte itself, and thus +introduce into the circuit chemical actions over and above those due to +the current. Faraday subjected these secondary actions to an exhaustive +examination. Instructed by his experiments, and rendered competent by +them to distinguish between primary and secondary results, he proceeds +to establish the doctrine of 'Definite Electro-chemical Decomposition.' + +Into the same circuit he introduced his voltameter, which consisted of +a graduated tube filled with acidulated water and provided with platinum +plates for the decomposition of the water, and also a cell containing +chloride of tin. Experiments already referred to had taught him that +this substance, though an insulator when solid, is a conductor when +fused, the passage of the current being always accompanied by the +decomposition of the chloride. He wished to ascertain what relation this +decomposition bore to that of the water in his voltameter. + +Completing his circuit, he permitted the current to continue until 'a +reasonable quantity of gas' was collected in the voltameter. The circuit +was then broken, and the quantity of tin liberated compared with the +quantity of gas. The weight of the former was 3.2 grains, that of the +latter 0.49742 of a grain. Oxygen, as you know, unites with hydrogen in +the proportion of 8 to 1, to form water. Calling the equivalent, or as +it is sometimes called, the atomic weight of hydrogen 1, that of oxygen +is 8; that of water is consequently 8 + 1 or 9. Now if the quantity of +water decomposed in Faraday's experiment be represented by the number 9, +or in other words by the equivalent of water, then the quantity of tin +liberated from the fused chloride is found by an easy calculation to be +57.9, which is almost exactly the chemical equivalent of tin. Thus both +the water and the chloride were broken up in proportions expressed +by their respective equivalents. The amount of electric force which +wrenched asunder the constituents of the molecule of water was +competent, and neither more nor less than competent, to wrench asunder +the constituents of the molecules of the chloride of tin. The fact +is typical. With the indications of his voltameter he compared the +decompositions of other substances, both singly and in series. He +submitted his conclusions to numberless tests. He purposely introduced +secondary actions. He endeavoured to hamper the fulfilment of those laws +which it was the intense desire of his mind to see established. But +from all these difficulties emerged the golden truth, that under every +variety of circumstances the decompositions of the voltaic current are +as definite in their character as those chemical combinations which gave +birth to the atomic theory. This law of Electro-chemical Decomposition +ranks, in point of importance, with that of Definite Combining +Proportions in chemistry. + + +Footnotes to Chapter 6 + + [1] I copy these words from the printed abstract of a Friday + evening lecture, given by myself, because they remind me of + Faraday's voice, responding to the utterance by an emphatic + 'hear! hear!'--Proceedings of the Royal Institution, vol. + ii. p. 132. + + [2] In 1838 he expresses himself thus:--'The word current is + so expressive in common language that when applied in the + consideration of electrical phenomena, we can hardly divest + it sufficiently of its meaning, or prevent our minds from + being prejudiced by it.'--Exp. Resear., vol. i. p. 515. ($ + 1617.) + + [3] This conclusion needs qualification. Faraday overlooked + the part played by ozone. + + + + +Chapter 7. + + Origin of power in the voltaic pile. + +In one of the public areas of the town of Como stands a statue with no +inscription on its pedestal, save that of a single name, 'Volta.' The +bearer of that name occupies a place for ever memorable in the history +of science. To him we owe the discovery of the voltaic pile, to which +for a brief interval we must now turn our attention. + +The objects of scientific thought being the passionless laws and +phenomena of external nature, one might suppose that their investigation +and discussion would be completely withdrawn from the region of the +feelings, and pursued by the cold dry light of the intellect alone. +This, however, is not always the case. Man carries his heart with him +into all his works. You cannot separate the moral and emotional from the +intellectual; and thus it is that the discussion of a point of science +may rise to the heat of a battle-field. The fight between the rival +optical theories of Emission and Undulation was of this fierce +character; and scarcely less fierce for many years was the contest as +to the origin and maintenance of the power of the voltaic pile. Volta +himself supposed it to reside in the Contact of different metals. +Here was exerted his 'Electro-motive force,' which tore the combined +electricities asunder and drove them as currents in opposite directions. +To render the circulation of the current possible, it was necessary to +connect the metals by a moist conductor; for when any two metals were +connected by a third, their relation to each other was such that a +complete neutralisation of the electric motion was the result. Volta's +theory of metallic contact was so clear, so beautiful, and apparently +so complete, that the best intellects of Europe accepted it as the +expression of natural law. + +Volta himself knew nothing of the chemical phenomena of the pile; but +as soon as these became known, suggestions and intimations appeared that +chemical action, and not metallic contact, might be the real source of +voltaic electricity. This idea was expressed by Fabroni in Italy, and +by Wollaston in England. It was developed and maintained by those +'admirable electricians,' Becquerel, of Paris, and De la Rive, of +Geneva. The Contact Theory, on the other hand, received its chief +development and illustration in Germany. It was long the scientific +creed of the great chemists and natural philosophers of that country, +and to the present hour there may be some of them unable to liberate +themselves from the fascination of their first-love. + +After the researches which I have endeavoured to place before you, it +was impossible for Faraday to avoid taking a side in this controversy. +He did so in a paper 'On the Electricity of the Voltaic Pile,' received +by the Royal Society on the 7th of April, 1834. His position in the +controversy might have been predicted. He saw chemical effects going +hand in hand with electrical effects, the one being proportional to the +other; and, in the paper now before us, he proved that when the former +was excluded, the latter were sought for in vain. He produced a current +without metallic contact; he discovered liquids which, though competent +to transmit the feeblest currents--competent therefore to allow the +electricity of contact to flow through them if it were able to form a +current--were absolutely powerless when chemically inactive. + +One of the very few experimental mistakes of Faraday occurred in +this investigation. He thought that with a single voltaic cell he +had obtained the spark before the metals touched, but he subsequently +discovered his error. To enable the voltaic spark to pass through air +before the terminals of the battery were united, it was necessary +to exalt the electro-motive force of the battery by multiplying its +elements; but all the elements Faraday possessed were unequal to the +task of urging the spark across the shortest measurable space of air. +Nor, indeed, could the action of the battery, the different metals of +which were in contact with each other, decide the point in question. +Still, as regards the identity of electricities from various sources, +it was at that day of great importance to determine whether or not +the voltaic current could jump, as a spark, across an interval before +contact. Faraday's friend, Mr. Gassiot, solved this problem. He erected +a battery of 4000 cells, and with it urged a stream of sparks from +terminal to terminal, when separated from each other by a measurable +space of air. + +The memoir on the 'Electricity of the Voltaic Pile,' published in 1834, +appears to have produced but little impression upon the supporters of +the contact theory. These indeed were men of too great intellectual +weight and insight lightly to take up, or lightly to abandon a theory. +Faraday therefore resumed the attack in a paper, communicated to the +Royal Society on the 6th of February, 1840. In this paper he hampered +his antagonists by a crowd of adverse experiments. He hung difficulty +after difficulty about the neck of the contact theory, until in its +efforts to escape from his assaults it so changed its character as to +become a thing totally different from the theory proposed by Volta. The +more persistently it was defended, however, the more clearly did it +show itself to be a congeries of devices, bearing the stamp of dialectic +skill rather than of natural truth. + +In conclusion, Faraday brought to bear upon it an argument which, had +its full weight and purport been understood at the time, would have +instantly decided the controversy. 'The contact theory,' he urged, +'assumed that a force which is able to overcome powerful resistance, +as for instance that of the conductors, good or bad, through which the +current passes, and that again of the electrolytic action where bodies +are decomposed by it, can arise out of nothing; that, without any change +in the acting matter, or the consumption of any generating force, a +current shall be produced which shall go on for ever against a constant +resistance, or only be stopped, as in the voltaic trough, by the ruins +which its exertion has heaped up in its own course. This would indeed be +a creation of power, and is like no other force in nature. We have many +processes by which the form of the power may be so changed, that an +apparent conversion of one into the other takes place. So we can change +chemical force into the electric current, or the current into chemical +force. The beautiful experiments of Seebeck and Peltier show the +convertibility of heat and electricity; and others by Oersted and myself +show the convertibility of electricity and magnetism. But in no case, +not even in those of the Gymnotus and Torpedo, is there a pure creation +or a production of power without a corresponding exhaustion of something +to supply it.' + +These words were published more than two years before either Mayer +printed his brief but celebrated essay on the Forces of Inorganic +Nature, or Mr. Joule published his first famous experiments on the +Mechanical Value of Heat. They illustrate the fact that before any great +scientific principle receives distinct enunciation by individuals, +it dwells more or less clearly in the general scientific mind. The +intellectual plateau is already high, and our discoverers are those who, +like peaks above the plateau, rise a little above the general level of +thought at the time. + +But many years prior even to the foregoing utterance of Faraday, a +similar argument had been employed. I quote here with equal pleasure +and admiration the following passage written by Dr. Roget so far back as +1829. Speaking of the contact theory, he says:--'If there could exist a +power having the property ascribed to it by the hypothesis, namely, +that of giving continual impulse to a fluid in one constant direction, +without being exhausted by its own action, it would differ essentially +from all the known powers in nature. All the powers and sources of +motion with the operation of which we are acquainted, when producing +these peculiar effects, are expended in the same proportion as those +effects are produced; and hence arises the impossibility of obtaining by +their agency a perpetual effect; or in other words a perpetual motion. +But the electro-motive force, ascribed by Volta to the metals, when in +contact, is a force which, as long as a free course is allowed to the +electricity it sets in motion, is never expended, and continues to be +excited with undiminished power in the production of a never-ceasing +effect. Against the truth of such a supposition the probabilities are +all but infinite.' When this argument, which he employed independently, +had clearly fixed itself in his mind, Faraday never cared to experiment +further on the source of electricity in the voltaic pile. The argument +appeared to him 'to remove the foundation itself of the contact theory,' +and he afterwards let it crumble down in peace.[1] + + +Footnote to Chapter 7 + + [1] To account for the electric current, which was really + the core of the whole discussion, Faraday demonstrated the + impotence of the Contact Theory as then enunciated and + defended. Still, it is certain that two different metals, + when brought into contact, charge themselves, the one with + positive and the other with negative electricity. I had the + pleasure of going over this ground with Kohlrausch in 1849, + and his experiments left no doubt upon my mind that the + contact electricity of Volta was a reality, though it could + produce no current. With one of the beautiful instruments + devised by himself, Sir William Thomson has rendered this + point capable of sure and easy demonstration; and he and + others now hold what may be called a contact theory, which, + while it takes into account the action of the metals, also + embraces the chemical phenomena of the circuit. Helmholtz, + I believe, was the first to give the contact theory this new + form, in his celebrated essay, Ueber die Erhaltung der + Kraft, p. 45. + + + + +Chapter 8. + + Researches on frictional electricity: induction: conduction: + specific inductive capacity: theory of contiguous particles. + +The burst of power which had filled the four preceding years with an +amount of experimental work unparalleled in the history of science +partially subsided in 1835, and the only scientific paper contributed +by Faraday in that year was a comparatively unimportant one, 'On an +improved Form of the Voltaic Battery.' He brooded for a time: his +experiments on electrolysis had long filled his mind; he looked, as +already stated, into the very heart of the electrolyte, endeavouring to +render the play of its atoms visible to his mental eye. He had no doubt +that in this case what is called 'the electric current' was propagated +from particle to particle of the electrolyte; he accepted the doctrine +of decomposition and recomposition which, according to Grothuss and +Davy, ran from electrode to electrode. And the thought impressed him +more and more that ordinary electric induction was also transmitted and +sustained by the action of 'contiguous particles.' + +His first great paper on frictional electricity was sent to the Royal +Society on November 30, 1837. We here find him face to face with an idea +which beset his mind throughout his whole subsequent life,--the idea of +action at a distance. It perplexed and bewildered him. In his attempts +to get rid of this perplexity, he was often unconsciously rebelling +against the limitations of the intellect itself. He loved to quote +Newton upon this point; over and over again he introduces his memorable +words, 'That gravity should be innate, inherent, and essential to +matter, so that one body may act upon another at a distance through a +vacuum and without the mediation of anything else, by and through which +this action and force may be conveyed from one to another, is to me +so great an absurdity, that I believe no man who has in philosophical +matters a competent faculty of thinking, can ever fall into it. Gravity +must be caused by an agent acting constantly according to certain laws; +but whether this agent be material or immaterial, I have left to the +consideration of my readers.'[1] + +Faraday does not see the same difficulty in his contiguous particles. +And yet, by transferring the conception from masses to particles, we +simply lessen size and distance, but we do not alter the quality of the +conception. Whatever difficulty the mind experiences in conceiving +of action at sensible distances, besets it also when it attempts to +conceive of action at insensible distances. Still the investigation of +the point whether electric and magnetic effects were wrought out through +the intervention of contiguous particles or not, had a physical interest +altogether apart from the metaphysical difficulty. Faraday grapples with +the subject experimentally. By simple intuition he sees that action at a +distance must be exerted in straight lines. Gravity, he knows, will not +turn a corner, but exerts its pull along a right line; hence his aim and +effort to ascertain whether electric action ever takes place in curved +lines. This once proved, it would follow that the action is carried on +by means of a medium surrounding the electrified bodies. His experiments +in 1837 reduced, in his opinion, this point of demonstration. He then +found that he could electrify, by induction, an insulated sphere placed +completely in the shadow of a body which screened it from direct action. +He pictured the lines of electric force bending round the edges of the +screen, and reuniting on the other side of it; and he proved that in +many cases the augmentation of the distance between his insulated sphere +and the inducing body, instead of lessening, increased the charge of +the sphere. This he ascribed to the coalescence of the lines of electric +force at some distance behind the screen. + +Faraday's theoretic views on this subject have not received general +acceptance, but they drove him to experiment, and experiment with him +was always prolific of results. By suitable arrangements he placed a +metallic sphere in the middle of a large hollow sphere, leaving a space +of something more than half an inch between them. The interior +sphere was insulated, the external one uninsulated. To the former he +communicated a definite charge of electricity. It acted by induction +upon the concave surface of the latter, and he examined how this act of +induction was effected by placing insulators of various kinds between +the two spheres. He tried gases, liquids, and solids, but the solids +alone gave him positive results. He constructed two instruments of the +foregoing description, equal in size and similar in form. The interior +sphere of each communicated with the external air by a brass stem ending +in a knob. The apparatus was virtually a Leyden jar, the two coatings of +which were the two spheres, with a thick and variable insulator between +them. The amount of charge in each jar was determined by bringing +a proof-plane into contact with its knob and measuring by a torsion +balance the charge taken away. He first charged one of his instruments, +and then dividing the charge with the other, found that when air +intervened in both cases the charge was equally divided. But when +shellac, sulphur, or spermaceti was interposed between the two spheres +of one jar, while air occupied this interval in the other, then he found +that the instrument occupied by the 'solid dielectric' takes more than +half the original charge. A portion of the charge was absorbed by +the dielectric itself. The electricity took time to penetrate the +dielectric. Immediately after the discharge of the apparatus, no trace +of electricity was found upon its knob. But after a time electricity was +found there, the charge having gradually returned from the dielectric +in which it had been lodged. Different insulators possess this power +of permitting the charge to enter them in different degrees. Faraday +figured their particles as polarized, and he concluded that the force of +induction is propagated from particle to particle of the dielectric from +the inner sphere to the outer one. This power of propagation possessed +by insulators he called their 'Specific Inductive Capacity.' + +Faraday visualizes with the utmost clearness the state of his contiguous +particles; one after another they become charged, each succeeding +particle depending for its charge upon its predecessor. And now he seeks +to break down the wall of partition between conductors and insulators. +'Can we not,' he says, 'by a gradual chain of association carry up +discharge from its occurrence in air through spermaceti and water, to +solutions, and then on to chlorides, oxides, and metals, without any +essential change in its character?' Even copper, he urges, offers +a resistance to the transmission of electricity. The action of its +particles differs from those of an insulator only in degree. They are +charged like the particles of the insulator, but they discharge with +greater ease and rapidity; and this rapidity of molecular discharge is +what we call conduction. Conduction then is always preceded by atomic +induction; and when, through some quality of the body which Faraday +does not define, the atomic discharge is rendered slow and difficult, +conduction passes into insulation. + +Though they are often obscure, a fine vein of philosophic thought runs +through those investigations. The mind of the philosopher dwells amid +those agencies which underlie the visible phenomena of Induction and +Conduction; and he tries by the strong light of his imagination to see +the very molecules of his dielectrics. It would, however, be easy to +criticise these researches, easy to show the looseness, and sometimes +the inaccuracy, of the phraseology employed; but this critical spirit +will get little good out of Faraday. Rather let those who ponder his +works seek to realise the object he set before him, not permitting +his occasional vagueness to interfere with their appreciation of his +speculations. We may see the ripples, and eddies, and vortices of a +flowing stream, without being able to resolve all these motions into +their constituent elements; and so it sometimes strikes me that Faraday +clearly saw the play of fluids and ethers and atoms, though his +previous training did not enable him to resolve what he saw into its +constituents, or describe it in a manner satisfactory to a mind versed +in mechanics. And then again occur, I confess, dark sayings, difficult +to be understood, which disturb my confidence in this conclusion. It +must, however, always be remembered that he works at the very boundaries +of our knowledge, and that his mind habitually dwells in the 'boundless +contiguity of shade' by which that knowledge is surrounded. + +In the researches now under review the ratio of speculation and +reasoning to experiment is far higher than in any of Faraday's previous +works. Amid much that is entangled and dark we have flashes of wondrous +insight and utterances which seem less the product of reasoning than of +revelation. I will confine myself here to one example of this divining +power. By his most ingenious device of a rapidly rotating mirror, +Wheatstone had proved that electricity required time to pass through +a wire, the current reaching the middle of the wire later than its +two ends. 'If,' says Faraday, 'the two ends of the wire in Professor +Wheatstone's experiments were immediately connected with two large +insulated metallic surfaces exposed to the air, so that the primary act +of induction, after making the contact for discharge, might be in part +removed from the internal portion of the wire at the first instance, +and disposed for the moment on its surface jointly with the air and +surrounding conductors, then I venture to anticipate that the middle +spark would be more retarded than before. And if those two plates were +the inner and outer coatings of a large jar or Leyden battery, then +the retardation of the spark would be much greater.' This was only +a prediction, for the experiment was not made.[2] Sixteen years +subsequently, however, the proper conditions came into play, and Faraday +was able to show that the observations of Werner Siemens, and Latimer +Clark, on subterraneous and submarine wires were illustrations, on a +grand scale, of the principle which he had enunciated in 1838. The wires +and the surrounding water act as a Leyden jar, and the retardation of +the current predicted by Faraday manifests itself in every message sent +by such cables. + +The meaning of Faraday in these memoirs on Induction and Conduction is, +as I have said, by no means always clear; and the difficulty will +be most felt by those who are best trained in ordinary theoretic +conceptions. He does not know the reader's needs, and he therefore +does not meet them. For instance he speaks over and over again of +the impossibility of charging a body with one electricity, though the +impossibility is by no means evident. The key to the difficulty is this. +He looks upon every insulated conductor as the inner coating of a Leyden +jar. An insulated sphere in the middle of a room is to his mind such a +coating; the walls are the outer coating, while the air between both is +the insulator, across which the charge acts by induction. Without this +reaction of the walls upon the sphere you could no more, according to +Faraday, charge it with electricity than you could charge a Leyden jar, +if its outer coating were removed. Distance with him is immaterial. His +strength as a generalizer enables him to dissolve the idea of magnitude; +and if you abolish the walls of the room--even the earth itself--he +would make the sun and planets the outer coating of his jar. I dare not +contend that Faraday in these memoirs made all his theoretic positions +good. But a pure vein of philosophy runs through these writings; while +his experiments and reasonings on the forms and phenomena of electrical +discharge are of imperishable importance. + + +Footnotes to Chapter 8 + + [1] Newton's third letter to Bentley. + + [2] Had Sir Charles Wheatstone been induced to resume his + measurements, varying the substances through which, and the + conditions under which, the current is propagated, he might + have rendered great service to science, both theoretic and + experimental. + + + + +Chapter 9. + + Rest needed--visit to Switzerland. + +The last of these memoirs was dated from the Royal Institution in June, +1838. It concludes the first volume of his 'Experimental Researches on +Electricity.' In 1840, as already stated, he made his final assault on +the Contact Theory, from which it never recovered.[1] He was now feeling +the effects of the mental strain to which he had been subjected for so +many years. During these years he repeatedly broke down. His wife alone +witnessed the extent of his prostration, and to her loving care we, and +the world, are indebted for the enjoyment of his presence here so long. +He found occasional relief in a theatre. He frequently quitted London +and went to Brighton and elsewhere, always choosing a situation which +commanded a view of the sea, or of some other pleasant horizon, where he +could sit and gaze and feel the gradual revival of the faith that + + 'Nature never did betray + The heart that loved her.' + +But very often for some days after his removal to the country, he would +be unable to do more than sit at a window and look out upon the sea and +sky. + +In 1841, his state became more serious than it had ever been before. A +published letter to Mr. Richard Taylor, dated March 11, 1843, contains +an allusion to his previous condition. 'You are aware,' he says, 'that +considerations regarding health have prevented me from working or +reading on science for the last two years.' This, at one period +or another of their lives, seems to be the fate of most great +investigators. They do not know the limits of their constitutional +strength until they have transgressed them. It is, perhaps, right that +they should transgress them, in order to ascertain where they lie. +Faraday, however, though he went far towards it, did not push his +transgression beyond his power of restitution. In 1841 Mrs. Faraday and +he went to Switzerland, under the affectionate charge of her brother, +Mr. George Barnard, the artist. This time of suffering throws fresh +light upon his character. I have said that sweetness and gentleness were +not its only constituents; that he was also fiery and strong. At the +time now referred to, his fire was low and his strength distilled away; +but the residue of his life was neither irritability nor discontent. He +was unfit to mingle in society, for conversation was a pain to him; but +let us observe the great Man-child when alone. He is at the village of +Interlaken, enjoying Jungfrau sunsets, and at times watching the Swiss +nailers making their nails. He keeps a little journal, in which he +describes the process of nailmaking, and incidentally throws a luminous +beam upon himself. + +'August 2, 1841.--Clout nailmaking goes on here rather considerably, and +is a very neat and pretty operation to observe. I love a smith's shop +and anything relating to smithery. My father was a smith.' + +From Interlaken he went to the Falls of the Giessbach, on the pleasant +lake of Brientz. And here we have him watching the shoot of the cataract +down its series of precipices. It is shattered into foam at the base of +each, and tossed by its own recoil as water-dust through the air. The +sun is at his back, shining on the drifting spray, and he thus describes +and muses on what he sees:-- + +'August 12, 1841.--To-day every fall was foaming from the abundance of +water, and the current of wind brought down by it was in some places too +strong to stand against. The sun shone brightly, and the rainbows seen +from various points were very beautiful. One at the bottom of a fine but +furious fall was very pleasant,--there it remained motionless, whilst +the gusts and clouds of spray swept furiously across its place and were +dashed against the rock. It looked like a spirit strong in faith and +steadfast in the midst of the storm of passions sweeping across it, and +though it might fade and revive, still it held on to the rock as in hope +and giving hope. And the very drops, which in the whirlwind of their +fury seemed as if they would carry all away, were made to revive it and +give it greater beauty.' + + +Footnote to Chapter 9 + + [1] See note, p. 77. + + + + +Chapter 10. + + Magnetization of light. + +But we must quit the man and go on to the discoverer: we shall return +for a brief space to his company by-and-by. Carry your thoughts back to +his last experiments, and see him endeavouring to prove that induction +is due to the action of contiguous particles. He knew that polarized +light was a most subtle and delicate investigator of molecular +condition. He used it in 1834 in exploring his electrolytes, and he +tried it in 1838 upon his dielectrics. At that time he coated two +opposite faces of a glass cube with tinfoil, connected one coating with +his powerful electric machine and the other with the earth, and examined +by polarized light the condition of the glass when thus subjected to +strong electric influence. He failed to obtain any effect; still he was +persuaded an action existed, and required only suitable means to call it +forth. + +After his return from Switzerland he was beset by these thoughts; they +were more inspired than logical: but he resorted to magnets and proved +his inspiration true. His dislike of 'doubtful knowledge' and his +efforts to liberate his mind from the thraldom of hypotheses have been +already referred to. Still this rebel against theory was incessantly +theorising himself. His principal researches are all connected by an +undercurrent of speculation. Theoretic ideas were the very sap of his +intellect--the source from which all his strength as an experimenter was +derived. While once sauntering with him through the Crystal Palace, at +Sydenham, I asked him what directed his attention to the magnetization +of light. It was his theoretic notions. He had certain views regarding +the unity and convertibility of natural forces; certain ideas regarding +the vibrations of light and their relations to the lines of magnetic +force; these views and ideas drove him to investigation. And so it must +always be: the great experimentalist must ever be the habitual theorist, +whether or not he gives to his theories formal enunciation. + +Faraday, you have been informed, endeavoured to improve the manufacture +of glass for optical purposes. But though he produced a heavy glass of +great refractive power, its value to optics did not repay him for +the pains and labour bestowed on it. Now, however, we reach a result +established by means of this same heavy glass, which made ample amends +for all. + +In November, 1845, he announced his discovery of the 'Magnetization of +Light and the Illumination of the Lines of Magnetic Force.' This title +provoked comment at the time, and caused misapprehension. He therefore +added an explanatory note; but the note left his meaning as entangled as +before. In fact Faraday had notions regarding the magnetization of light +which were peculiar to himself, and untranslatable into the scientific +language of the time. Probably no other philosopher of his day would +have employed the phrases just quoted as appropriate to the discovery +announced in 1845. But Faraday was more than a philosopher; he was +a prophet, and often wrought by an inspiration to be understood by +sympathy alone. The prophetic element in his character occasionally +coloured, and even injured, the utterance of the man of science; +but subtracting that element, though you might have conferred on him +intellectual symmetry, you would have destroyed his motive force. + +But let us pass from the label of this casket to the jewel it +contains. 'I have long,' he says, 'held an opinion, almost amounting +to conviction, in common, I believe, with many other lovers of natural +knowledge, that the various forms under which the forces of matter are +made manifest have one common origin; in other words, are so directly +related and mutually dependent, that they are convertible, as it were, +into one another, and possess equivalents of power in their action.... +This strong persuasion,' he adds, 'extended to the powers of light.' +And then he examines the action of magnets upon light. From conversation +with him and Anderson, I should infer that the labour preceding this +discovery was very great. The world knows little of the toil of the +discoverer. It sees the climber jubilant on the mountain top, but +does not know the labour expended in reaching it. Probably hundreds of +experiments had been made on transparent crystals before he thought of +testing his heavy glass. Here is his own clear and simple description +of the result of his first experiment with this substance:--'A piece of +this glass, about two inches square, and 0.5 of an inch thick, having +flat and polished edges, was placed as a diamagnetic[1] between the +poles (not as yet magnetized by the electric current), so that the +polarized ray should pass through its length; the glass acted as air, +water, or any other transparent substance would do; and if the eye-piece +were previously turned into such a position that the polarized ray was +extinguished, or rather the image produced by it rendered invisible, +then the introduction of the glass made no alteration in this respect. +In this state of circumstances, the force of the electro-magnet +was developed by sending an electric current through its coils, and +immediately the image of the lamp-flame became visible and continued so +as long as the arrangement continued magnetic. On stopping the electric +current, and so causing the magnetic force to cease, the light instantly +disappeared. These phenomena could be renewed at pleasure, at any +instant of time, and upon any occasion, showing a perfect dependence of +cause and effect.' + +In a beam of ordinary light the particles of the luminiferous ether +vibrate in all directions perpendicular to the line of progression; by +the act of polarization, performed here by Faraday, all oscillations +but those parallel to a certain plane are eliminated. When the plane +of vibration of the polarizer coincides with that of the analyzer, a +portion of the beam passes through both; but when these two planes +are at right angles to each other, the beam is extinguished. If by any +means, while the polarizer and analyzer remain thus crossed, the plane +of vibration of the polarized beam between them could be changed, +then the light would be, in part at least, transmitted. In Faraday's +experiment this was accomplished. His magnet turned the plane of +polarization of the beam through a certain angle, and thus enabled it +to get through the analyzer; so that 'the magnetization of light and the +illumination of the magnetic lines of force' becomes, when expressed +in the language of modern theory, the rotation of the plane of +polarization. + +To him, as to all true philosophers, the main value of a fact was its +position and suggestiveness in the general sequence of scientific truth. +Hence, having established the existence of a phenomenon, his habit +was to look at it from all possible points of view, and to develop its +relationship to other phenomena. He proved that the direction of the +rotation depends upon the polarity of his magnet; being reversed when +the magnetic poles are reversed. He showed that when a polarized ray +passed through his heavy glass in a direction parallel to the magnetic +lines of force, the rotation is a maximum, and that when the direction +of the ray is at right angles to the lines of force, there is no +rotation at all. He also proved that the amount of the rotation is +proportional to the length of the diamagnetic through which the ray +passes. He operated with liquids and solutions. Of aqueous solutions he +tried 150 and more, and found the power in all of them. He then examined +gases; but here all his efforts to produce any sensible action upon +the polarized beam were ineffectual. He then passed from magnets to +currents, enclosing bars of heavy glass, and tubes containing liquids +and aqueous solutions within an electro-magnetic helix. A current sent +through the helix caused the plane of polarization to rotate, and always +in the direction of the current. The rotation was reversed when the +current was reversed. In the case of magnets, he observed a gradual, +though quick, ascent of the transmitted beam from a state of darkness +to its maximum brilliancy, when the magnet was excited. In the case of +currents, the beam attained at once its maximum. This he showed to be +due to the time required by the iron of the electro-magnet to assume its +full magnetic power, which time vanishes when a current, without iron, +is employed. 'In this experiment,' he says, 'we may, I think, justly +say that a ray of light is electrified, and the electric forces +illuminated.' In the helix, as with the magnets, he submitted air to +magnetic influence 'carefully and anxiously,' but could not discover any +trace of action on the polarized ray. + +Many substances possess the power of turning the plane of polarization +without the intervention of magnetism. Oil of turpentine and quartz +are examples; but Faraday showed that, while in one direction, that is, +across the lines of magnetic force, his rotation is zero, augmenting +gradually from this until it attains its maximum, when the direction of +the ray is parallel to the lines of force; in the oil of turpentine the +rotation is independent of the direction of the ray. But he showed that +a still more profound distinction exists between the magnetic rotation +and the natural one. I will try to explain how. Suppose a tube with +glass ends containing oil of turpentine to be placed north and south. +Fixing the eye at the south end of the tube, let a polarized beam be +sent through it from the north. To the observer in this position +the rotation of the plane of polarization, by the turpentine, is +right-handed. Let the eye be placed at the north end of the tube, and +a beam be sent through it from the south; the rotation is still +right-handed. Not so, however, when a bar of heavy glass is subjected +to the action of an electric current. In this case if, in the first +position of the eye, the rotation be right-handed, in the second +position it is left-handed. These considerations make it manifest that +if a polarized beam, after having passed through the oil of turpentine +in its natural state, could by any means be reflected back through the +liquid, the rotation impressed upon the direct beam would be exactly +neutralized by that impressed upon the reflected one. Not so with the +induced magnetic effect. Here it is manifest that the rotation would +be doubled by the act of reflection. Hence Faraday concludes that the +particles of the oil of turpentine which rotate by virtue of their +natural force, and those which rotate in virtue of the induced force, +cannot be in the same condition. The same remark applies to all bodies +which possess a natural power of rotating the plane of polarization. + +And then he proceeded with exquisite skill and insight to take advantage +of this conclusion. He silvered the ends of his piece of heavy glass, +leaving, however, a narrow portion parallel to two edges diagonally +opposed to each other unsilvered. He then sent his beam through this +uncovered portion, and by suitably inclining his glass caused the beam +within it to reach his eye first direct, and then after two, four, and +six reflections. These corresponded to the passage of the ray once, +three times, five times, and seven times through the glass. He thus +established with numerical accuracy the exact proportionality of the +rotation to the distance traversed by the polarized beam. Thus in one +series of experiments where the rotation required by the direct beam +was 12degrees, that acquired by three passages through the glass was +36degrees, while that acquired by five passages was 60degrees. But even +when this method of magnifying was applied, he failed with various +solid substances to obtain any effect; and in the case of air, though he +employed to the utmost the power which these repeated reflections placed +in his hands, he failed to produce the slightest sensible rotation. + +These failures of Faraday to obtain the effect with gases seem to +indicate the true seat of the phenomenon. The luminiferous ether +surrounds and is influenced by the ultimate particles of matter. The +symmetry of the one involves that of the other. Thus, if the molecules +of a crystal be perfectly symmetrical round any line through the +crystal, we may safely conclude that a ray will pass along this line +as through ordinary glass. It will not be doubly refracted. From the +symmetry of the liquid figures, known to be produced in the planes of +freezing, when radiant heat is sent through ice, we may safely infer +symmetry of aggregation, and hence conclude that the line perpendicular +to the planes of freezing is a line of no double refraction; that it is, +in fact, the optic axis of the crystal. The same remark applies to the +line joining the opposite blunt angles of a crystal of Iceland spar. +The arrangement of the molecules round this line being symmetrical, +the condition of the ether depending upon these molecules shares their +symmetry; and there is, therefore, no reason why the wavelength should +alter with the alteration of the azimuth round this line. Annealed glass +has its molecules symmetrically arranged round every line that can +be drawn through it; hence it is not doubly refractive. But let the +substance be either squeezed or strained in one direction, the molecular +symmetry, and with it the symmetry of the ether, is immediately +destroyed and the glass becomes doubly refractive. Unequal heating +produces the same effect. Thus mechanical strains reveal themselves by +optical effects; and there is little doubt that in Faraday's experiment +it is the magnetic strain that produces the rotation of the plane of +polarization.[2] + + +Footnotes to Chapter 10 + + [1] 'By a diamagnetic,' says Faraday, 'I mean a body through + which lines of magnetic force are passing, and which does + not by their action assume the usual magnetic state of iron + or loadstone.' Faraday subsequently used this term in a + different sense from that here given, as will immediately + appear. + + [2] The power of double refraction conferred on the centre + of a glass rod, when it is caused to sound the fundamental + note due to its longitudinal vibration, and the absence of + the same power in the case of vibrating air (enclosed in a + glass organ-pipe), seems to be analogous to the presence and + absence of Faraday's effect in the same two substances. + Faraday never, to my knowledge, attempted to give, even in + conversation, a picture of the molecular condition of his + heavy glass when subjected to magnetic influence. In a + mathematical investigation of the subject, published in the + Proceedings of the Royal Society for 1856, Sir William + Thomson arrives at the conclusion that the 'diamagnetic' is + in a state of molecular rotation. + + + + +Chapter 11. + + Discovery of diamagnetism--researches on magne-crystallic + action. + +Faraday's next great step in discovery was announced in a memoir on the +'Magnetic Condition of all matter,' communicated to the Royal Society on +December 18, 1845. One great source of his success was the employment +of extraordinary power. As already stated, he never accepted a negative +answer to an experiment until he had brought to bear upon it all the +force at his command. He had over and over again tried steel magnets and +ordinary electro-magnets on various substances, but without detecting +anything different from the ordinary attraction exhibited by a few of +them. Stronger coercion, however, developed a new action. Before the +pole of an electro-magnet, he suspended a fragment of his famous heavy +glass; and observed that when the magnet was powerfully excited the +glass fairly retreated from the pole. It was a clear case of magnetic +repulsion. He then suspended a bar of the glass between two poles; +the bar retreated when the poles were excited, and set its length +equatorially or at right angles to the line joining them. When an +ordinary magnetic body was similarly suspended, it always set axially, +that is, from pole to pole. + +Faraday called those bodies which were repelled by the poles of a +magnet, diamagnetic bodies; using this term in a sense different from +that in which he employed it in his memoir on the magnetization of +light. The term magnetic he reserved for bodies which exhibited the +ordinary attraction. He afterwards employed the term magnetic to cover +the whole phenomena of attraction and repulsion, and used the word +paramagnetic to designate such magnetic action as is exhibited by iron. + +Isolated observations by Brugmanns, Becquerel, Le Baillif, Saigy, and +Seebeck had indicated the existence of a repulsive force exercised by +the magnet on two or three substances; but these observations, which +were unknown to Faraday, had been permitted to remain without extension +or examination. Having laid hold of the fact of repulsion, Faraday +immediately expanded and multiplied it. He subjected bodies of the most +varied qualities to the action of his magnet:--mineral salts, acids, +alkalis, ethers, alcohols, aqueous solutions, glass, phosphorus, +resins, oils, essences, vegetable and animal tissues, and found them +all amenable to magnetic influence. No known solid or liquid proved +insensible to the magnetic power when developed in sufficient strength. +All the tissues of the human body, the blood--though it contains +iron--included, were proved to be diamagnetic. So that if you could +suspend a man between the poles of a magnet, his extremities would +retreat from the poles until his length became equatorial. + +Soon after he had commenced his researches on diamagnetism, Faraday +noticed a remarkable phenomenon which first crossed my own path in the +following way: In the year 1849, while working in the cabinet of my +friend, Professor Knoblauch, of Marburg, I suspended a small copper coin +between the poles of an electro-magnet. On exciting the magnet, the coin +moved towards the poles and then suddenly stopped, as if it had struck +against a cushion. On breaking the circuit, the coin was repelled, the +revulsion being so violent as to cause it to spin several times round +its axis of suspension. A Silber-groschen similarly suspended exhibited +the same deportment. For a moment I thought this a new discovery; but on +looking over the literature of the subject, it appeared that Faraday +had observed, multiplied, and explained the same effect during his +researches on diamagnetism. His explanation was based upon his own great +discovery of magneto-electric currents. The effect is a most singular +one. A weight of several pounds of copper may be set spinning between +the electro-magnetic poles; the excitement of the magnet instantly stops +the rotation. Though nothing is apparent to the eye, the copper, if +moved in the excited magnetic field, appears to move through a viscous +fluid; while, when a flat piece of the metal is caused to pass to and +fro like a saw between the poles, the sawing of the magnetic field +resembles the cutting through of cheese or butter.[1] This virtual +friction of the magnetic field is so strong, that copper, by its rapid +rotation between the poles, might probably be fused. We may easily +dismiss this experiment by saying that the heat is due to the electric +currents excited in the copper. But so long as we are unable to reply +to the question, 'What is an electric current?' the explanation is only +provisional. For my own part, I look with profound interest and hope on +the strange action here referred to. + +Faraday's thoughts ran intuitively into experimental combinations, +so that subjects whose capacity for experimental treatment would, to +ordinary minds, seem to be exhausted in a moment, were shown by him to +be all but inexhaustible. He has now an object in view, the first step +towards which is the proof that the principle of Archimedes is true of +magnetism. He forms magnetic solutions of various degrees of strength, +places them between the poles of his magnet, and suspends in the +solutions various magnetic bodies. He proves that when the solution +is stronger than the body plunged in it, the body, though magnetic, +is repelled; and when an elongated piece of it is surrounded by the +solution, it sets, like a diamagnetic body, equatorially between the +excited poles. The same body when suspended in a solution of weaker +magnetic power than itself, is attracted as a whole, while an elongated +portion of it sets axially. + +And now theoretic questions rush in upon him. Is this new force a true +repulsion, or is it merely a differential attraction? Might not the +apparent repulsion of diamagnetic bodies be really due to the greater +attraction of the medium by which they are surrounded? He tries the +rarefaction of air, but finds the effect insensible. He is averse to +ascribing a capacity of attraction to space, or to any hypothetical +medium supposed to fill space. He therefore inclines, but still with +caution, to the opinion that the action of a magnet upon bismuth is a +true and absolute repulsion, and not merely the result of differential +attraction. And then he clearly states a theoretic view sufficient to +account for the phenomena. 'Theoretically,' he says, 'an explanation of +the movements of the diamagnetic bodies, and all the dynamic phenomena +consequent upon the action of magnets upon them, might be offered in the +supposition that magnetic induction caused in them a contrary state to +that which it produced in ordinary matter.' That is to say, while in +ordinary magnetic influence the exciting pole excites adjacent to itself +the contrary magnetism, in diamagnetic bodies the adjacent magnetism is +the same as that of the exciting pole. This theory of reversed polarity, +however, does not appear to have ever laid deep hold of Faraday's mind; +and his own experiments failed to give any evidence of its truth. He +therefore subsequently abandoned it, and maintained the non-polarity of +the diamagnetic force. + +He then entered a new, though related field of inquiry. Having dealt +with the metals and their compounds, and having classified all of +them that came within the range of his observation under the two heads +magnetic and diamagnetic, he began the investigation of the phenomena +presented by crystals when subjected to magnetic power. This action of +crystals had been in part theoretically predicted by Poisson,[2] and +actually discovered by Plucker, whose beautiful results, at the period +which we have now reached, profoundly interested all scientific men. +Faraday had been frequently puzzled by the deportment of bismuth, a +highly crystalline metal. Sometimes elongated masses of the substance +refused to set equatorially, sometimes they set persistently oblique, +and sometimes even, like a magnetic body, from pole to pole. + +'The effect,' he says, 'occurs at a single pole; and it is then striking +to observe a long piece of a substance so diamagnetic as bismuth +repelled, and yet at the same moment set round with force, axially, or +end on, as a piece of magnetic substance would do.' The effect perplexed +him; and in his efforts to release himself from this perplexity, no +feature of this new manifestation of force escaped his attention. His +experiments are described in a memoir communicated to the Royal Society +on December 7, 1848. + +I have worked long myself at magne-crystallic action, amid all the light +of Faraday's and Plucker's researches. The papers now before me were +objects of daily and nightly study with me eighteen or nineteen years +ago; but even now, though their perusal is but the last of a series of +repetitions, they astonish me. Every circumstance connected with the +subject; every shade of deportment; every variation in the energy of +the action; almost every application which could possibly be made of +magnetism to bring out in detail the character of this new force, +is minutely described. The field is swept clean, and hardly anything +experimental is left for the gleaner. The phenomena, he concludes, are +altogether different from those of magnetism or diamagnetism: they would +appear, in fact, to present to us 'a new force, or a new form of force, +in the molecules of matter,' which, for convenience sake, he designates +by a new word, as 'the magne-crystallic force.' + +He looks at the crystal acted upon by the magnet. From its mass he +passes, in idea, to its atoms, and he asks himself whether the power +which can thus seize upon the crystalline molecules, after they have +been fixed in their proper positions by crystallizing force, may +not, when they are free, be able to determine their arrangement? He, +therefore, liberates the atoms by fusing the bismuth. He places the +fused substance between the poles of an electro-magnet, powerfully +excited; but he fails to detect any action. I think it cannot be doubted +that an action is exerted here, that a true cause comes into play; but +its magnitude is not such as sensibly to interfere with the force of +crystallization, which, in comparison with the diamagnetic force, is +enormous. 'Perhaps,' adds Faraday, 'if a longer time were allowed, and +a permanent magnet used, a better result might be obtained. I had built +many hopes upon the process.' This expression, and his writings +abound in such, illustrates what has been already said regarding his +experiments being suggested and guided by his theoretic conceptions. His +mind was full of hopes and hypotheses, but he always brought them to an +experimental test. The record of his planned and executed experiments +would, I doubt not, show a high ratio of hopes disappointed to hopes +fulfilled; but every case of fulfilment abolished all memory of defeat; +disappointment was swallowed up in victory. + +After the description of the general character of this new force, +Faraday states with the emphasis here reproduced its mode of +action: 'The law of action appears to be that the line or axis of +MAGNE-CRYSTALLIC force (being the resultant of the action of all the +molecules) tends to place itself parallel, or as a tangent, to the +magnetic curve, or line of magnetic force, passing through the place +where the crystal is situated.' The magne-crystallic force, moreover, +appears to him 'to be clearly distinguished from the magnetic or +diamagnetic forces, in that it causes neither approach nor recession, +consisting not in attraction or repulsion, but in giving a certain +determinate position to the mass under its influence.' And then he goes +on 'very carefully to examine and prove the conclusion that there was no +connection of the force with attractive or repulsive influences.' With +the most refined ingenuity he shows that, under certain circumstances, +the magne-crystallic force can cause the centre of gravity of a highly +magnetic body to retreat from the poles, and the centre of gravity of a +highly diamagnetic body to approach them. His experiments root his mind +more and more firmly in the conclusion that 'neither attraction nor +repulsion causes the set, or governs the final position' of the crystal +in the magnetic field. That the force which does so is therefore +'distinct in its character and effects from the magnetic and diamagnetic +forms of force. On the other hand,' he continues, 'it has a most +manifest relation to the crystalline structure of bismuth and other +bodies, and therefore to the power by which their molecules are able to +build up the crystalline masses.' + +And here follows one of those expressions which characterize the +conceptions of Faraday in regard to force generally:--'It appears to me +impossible to conceive of the results in any other way than by a mutual +reaction of the magnetic force, and the force of the particles of the +crystals upon each other.' He proves that the action of the force, +though thus molecular, is an action at a distance; he shows that a +bismuth crystal can cause a freely suspended magnetic needle to set +parallel to its magne-crystallic axis. Few living men are aware of the +difficulty of obtaining results like this, or of the delicacy necessary +to their attainment. 'But though it thus takes up the character of +a force acting at a distance, still it is due to that power of the +particles which makes them cohere in regular order and gives the mass +its crystalline aggregation, which we call at other times the +attraction of aggregation, and so often speak of as acting at insensible +distances.' Thus he broods over this new force, and looks at it from all +possible points of inspection. Experiment follows experiment, as thought +follows thought. He will not relinquish the subject as long as a hope +exists of throwing more light upon it. He knows full well the anomalous +nature of the conclusion to which his experiments lead him. But +experiment to him is final, and he will not shrink from the conclusion. +'This force,' he says, 'appears to me to be very strange and striking +in its character. It is not polar, for there is no attraction +or repulsion.' And then, as if startled by his own utterance, he +asks--'What is the nature of the mechanical force which turns the +crystal round, and makes it affect a magnet?'... 'I do not remember,' he +continues 'heretofore such a case of force as the present one, where a +body is brought into position only, without attraction or repulsion.' + +Plucker, the celebrated geometer already mentioned, who pursued +experimental physics for many years of his life with singular devotion +and success, visited Faraday in those days, and repeated before him +his beautiful experiments on magneto-optic action. Faraday repeated and +verified Plucker's observations, and concluded, what he at first seemed +to doubt, that Plucker's results and magne-crystallic action had the +same origin. + +At the end of his papers, when he takes a last look along the line of +research, and then turns his eyes to the future, utterances quite as +much emotional as scientific escape from Faraday. 'I cannot,' he says, +at the end of his first paper on magne-crystallic action, 'conclude +this series of researches without remarking how rapidly the knowledge of +molecular forces grows upon us, and how strikingly every investigation +tends to develop more and more their importance, and their extreme +attraction as an object of study. A few years ago magnetism was to us an +occult power, affecting only a few bodies, now it is found to influence +all bodies, and to possess the most intimate relations with electricity, +heat, chemical action, light, crystallization, and through it, with +the forces concerned in cohesion; and we may, in the present state of +things, well feel urged to continue in our labours, encouraged by the +hope of bringing it into a bond of union with gravity itself.' + + +Supplementary remarks + +A brief space will, perhaps, be granted me here to state the further +progress of an investigation which interested Faraday so much. Drawn by +the fame of Bunsen as a teacher, in the year 1848 I became a student in +the University of Marburg, in Hesse Cassel. Bunsen's behaviour to me +was that of a brother as well as that of a teacher, and it was also my +happiness to make the acquaintance and gain the friendship of Professor +Knoblauch, so highly distinguished by his researches on Radiant Heat. +Plucker's and Faraday's investigations filled all minds at the time, +and towards the end of 1849, Professor Knoblauch and myself commenced +a joint investigation of the entire question. Long discipline was +necessary to give us due mastery over it. Employing a method proposed by +Dove, we examined the optical properties of our crystals ourselves; +and these optical observations went hand in hand with our magnetic +experiments. The number of these experiments was very great, but for +a considerable time no fact of importance was added to those already +published. At length, however, it was our fortune to meet with various +crystals whose deportment could not be brought under the laws of +magne-crystallic action enunciated by Plucker. We also discovered +instances which led us to suppose that the magne-crystallic force was +by no means independent, as alleged, of the magnetism or diamagnetism of +the mass of the crystal. Indeed, the more we worked at the subject, the +more clearly did it appear to us that the deportment of crystals in the +magnetic field was due, not to a force previously unknown, but to +the modification of the known forces of magnetism and diamagnetism by +crystalline aggregation. + +An eminent example of magne-crystallic action adduced by Plucker, and +experimented on by Faraday, was Iceland spar. It is what in optics is +called a negative crystal, and according to the law of Plucker, the axis +of such a crystal was always repelled by a magnet. But we showed that it +was only necessary to substitute, in whole or in part, carbonate of iron +for carbonate of lime, thus changing the magnetic but not the optical +character of the crystal, to cause the axis to be attracted. That the +deportment of magnetic crystals is exactly antithetical to that of +diamagnetic crystals isomorphous with the magnetic ones, was proved +to be a general law of action. In all cases, the line which in +a diamagnetic crystal set equatorially, always set itself in an +isomorphous magnetic crystal axially. By mechanical compression other +bodies were also made to imitate the Iceland spar. + +These and numerous other results bearing upon the question were +published at the time in the 'Philosophical Magazine' and in +'Poggendorff's Annalen'; and the investigation of diamagnetism and +magne-crystallic action was subsequently continued by me in the +laboratory of Professor Magnus of Berlin. In December, 1851, after I had +quitted Germany, Dr. Bence Jones went to the Prussian capital to see +the celebrated experiments of Du Bois Reymond. Influenced, I suppose, by +what he there heard, he afterwards invited me to give a Friday evening +discourse at the Royal Institution. I consented, not without fear and +trembling. For the Royal Institution was to me a kind of dragon's den, +where tact and strength would be necessary to save me from destruction. +On February 11, 1853, the discourse was given, and it ended happily. +I allude to these things, that I may mention that, though my aim and +object in that lecture was to subvert the notions both of Faraday and +Plucker, and to establish in opposition to their views what I regarded +as the truth, it was very far from producing in Faraday either enmity or +anger. At the conclusion of the lecture, he quitted his accustomed seat, +crossed the theatre to the corner into which I had shrunk, shook me by +the hand, and brought me back to the table. Once more, subsequently, +and in connection with a related question, I ventured to differ from him +still more emphatically. It was done out of trust in the greatness of +his character; nor was the trust misplaced. He felt my public dissent +from him; and it pained me afterwards to the quick to think that I had +given him even momentary annoyance. It was, however, only momentary. His +soul was above all littleness and proof to all egotism. He was the same +to me afterwards that he had been before; the very chance expression +which led me to conclude that he felt my dissent being one of kindness +and affection. + +It required long subsequent effort to subdue the complications of +magne-crystallic action, and to bring under the dominion of elementary +principles the vast mass of facts which the experiments of Faraday and +Plucker had brought to light. It was proved by Reich, Edmond Becquerel, +and myself, that the condition of diamagnetic bodies, in virtue of which +they were repelled by the poles of a magnet, was excited in them by +those poles; that the strength of this condition rose and fell with, and +was proportional to, the strength of the acting magnet. It was not then +any property possessed permanently by the bismuth, and which merely +required the development of magnetism to act upon it, that caused the +repulsion; for then the repulsion would have been simply proportional to +the strength of the influencing magnet, whereas experiment proved it to +augment as the square of the strength. The capacity to be repelled was +therefore not inherent in the bismuth, but induced. So far an identity +of action was established between magnetic and diamagnetic bodies. +After this the deportment of magnetic bodies, 'normal' and 'abnormal'; +crystalline, amorphous, and compressed, was compared with that of +crystalline, amorphous, and compressed diamagnetic bodies; and by a +series of experiments, executed in the laboratory of this Institution, +the most complete antithesis was established between magnetism and +diamagnetism. This antithesis embraced the quality of polarity,--the +theory of reversed polarity, first propounded by Faraday, being proved +to be true. The discussion of the question was very brisk. On the +Continent Professor Wilhelm Weber was the ablest and most successful +supporter of the doctrine of diamagnetic polarity; and it was with an +apparatus, devised by him and constructed under his own superintendence, +by Leyser of Leipzig, that the last demands of the opponents of +diamagnetic polarity were satisfied. The establishment of this point was +absolutely necessary to the explanation of magne-crystallic action. + +With that admirable instinct which always guided him, Faraday had seen +that it was possible, if not probable, that the diamagnetic force acts +with different degrees of intensity in different directions, through +the mass of a crystal. In his studies on electricity, he had sought an +experimental reply to the question whether crystalline bodies had not +different specific inductive capacities in different directions, but +he failed to establish any difference of the kind. His first attempt +to establish differences of diamagnetic action in different directions +through bismuth, was also a failure; but he must have felt this to be +a point of cardinal importance, for he returned to the subject in 1850, +and proved that bismuth was repelled with different degrees of force in +different directions. It seemed as if the crystal were compounded of +two diamagnetic bodies of different strengths, the substance being more +strongly repelled across the magne-crystallic axis than along it. The +same result was obtained independently, and extended to various +other bodies, magnetic as well as diamagnetic, and also to compressed +substances, a little subsequently by myself. + +The law of action in relation to this point is, that in diamagnetic +crystals, the line along which the repulsion is a maximum, sets +equatorially in the magnetic field; while in magnetic crystals the line +along which the attraction is a maximum sets from pole to pole. Faraday +had said that the magne-crystallic force was neither attraction nor +repulsion. Thus far he was right. It was neither taken singly, but it +was both. By the combination of the doctrine of diamagnetic polarity +with these differential attractions and repulsions, and by paying due +regard to the character of the magnetic field, every fact brought +to light in the domain of magne-crystallic action received complete +explanation. The most perplexing of those facts were shown to result +from the action of mechanical couples, which the proved polarity both +of magnetism and diamagnetism brought into play. Indeed the thoroughness +with which the experiments of Faraday were thus explained, is the most +striking possible demonstration of the marvellous precision with which +they were executed. + + +Footnotes to Chapter 11 + + [1] See Heat as a Mode of Motion, ninth edition, p. 75. + + [2] See Sir Wm. Thomson on Magne-crystallic Action. Phil. + Mag., 1851. + + + + +Chapter 12. + + Magnetism of flame and gases--atmospheric magnetism + +When an experimental result was obtained by Faraday it was instantly +enlarged by his imagination. I am acquainted with no mind whose power +and suddenness of expansion at the touch of new physical truth could be +ranked with his. Sometimes I have compared the action of his experiments +on his mind to that of highly combustible matter thrown into a furnace; +every fresh entry of fact was accompanied by the immediate development +of light and heat. The light, which was intellectual, enabled him to see +far beyond the boundaries of the fact itself, and the heat, which was +emotional, urged him to the conquest of this newly-revealed domain. But +though the force of his imagination was enormous, he bridled it like a +mighty rider, and never permitted his intellect to be overthrown. + +In virtue of the expansive power which his vivid imagination conferred +upon him, he rose from the smallest beginnings to the grandest ends. +Having heard from Zantedeschi that Bancalari had established the +magnetism of flame, he repeated the experiments and augmented the +results. He passed from flames to gases, examining and revealing their +magnetic and diamagnetic powers; and then he suddenly rose from his +bubbles of oxygen and nitrogen to the atmospheric envelope of the +earth itself, and its relations to the great question of terrestrial +magnetism. The rapidity with which these ever-augmenting thoughts +assumed the form of experiments is unparalleled. His power in this +respect is often best illustrated by his minor investigations, and, +perhaps, by none more strikingly than by his paper 'On the Diamagnetic +Condition of Flame and Gases,' published as a letter to Mr. Richard +Taylor, in the 'Philosophical Magazine' for December, 1847. After +verifying, varying, and expanding the results of Bancalari, he submitted +to examination heated air-currents, produced by platinum spirals placed +in the magnetic field, and raised to incandescence by electricity. He +then examined the magnetic deportment of gases generally. Almost all +of these gases are invisible; but he must, nevertheless, track them in +their unseen courses. He could not effect this by mingling smoke with +his gases, for the action of his magnet upon the smoke would have +troubled his conclusions. He, therefore, 'caught' his gases in tubes, +carried them out of the magnetic field, and made them reveal themselves +at a distance from the magnet. + +Immersing one gas in another, he determined their differential action; +results of the utmost beauty being thus arrived at. Perhaps the +most important are those obtained with atmospheric air and its two +constituents. Oxygen, in various media, was strongly attracted by the +magnet; in coal-gas, for example, it was powerfully magnetic, whereas +nitrogen was diamagnetic. Some of the effects obtained with oxygen +in coal-gas were strikingly beautiful. When the fumes of chloride of +ammonium (a diamagnetic substance) were mingled with the oxygen, the +cloud of chloride behaved in a most singular manner,--'The attraction +of iron filings,' says Faraday, 'to a magnetic pole is not more striking +than the appearance presented by the oxygen under these circumstances.' + +On observing this deportment the question immediately occurs to +him,--Can we not separate the oxygen of the atmosphere from its nitrogen +by magnetic analysis? It is the perpetual occurrence of such questions +that marks the great experimenter. The attempt to analyze atmospheric +air by magnetic force proved a failure, like the previous attempt to +influence crystallization by the magnet. The enormous comparative power +of the force of crystallization I have already assigned as a reason for +the incompetence of the magnet to determine molecular arrangement; in +the present instance the magnetic analysis is opposed by the force of +diffusion, which is also very strong comparatively. The same remark +applies to, and is illustrated by, another experiment subsequently +executed by Faraday. Water is diamagnetic, sulphate of iron is strongly +magnetic. He enclosed 'a dilute solution of sulphate of iron in a tube, +and placed the lower end of the tube between the poles of a powerful +horseshoe magnet for days together,' but he could produce 'no +concentration of the solution in the part near the magnet.' Here also +the diffusibility of the salt was too powerful for the force brought +against it. + +The experiment last referred to is recorded in a paper presented to +the Royal Society on the 2nd August, 1850, in which he pursues the +investigation of the magnetism of gases. Newton's observations on +soap-bubbles were often referred to by Faraday. His delight in a +soap-bubble was like that of a boy, and he often introduced them into +his lectures, causing them, when filled with air, to float on invisible +seas of carbonic acid, and otherwise employing them as a means of +illustration. He now finds them exceedingly useful in his experiments +on the magnetic condition of gases. A bubble of air in a magnetic field +occupied by air was unaffected, save through the feeble repulsion of its +envelope. A bubble of nitrogen, on the contrary, was repelled from the +magnetic axis with a force far surpassing that of a bubble of air. +The deportment of oxygen in air 'was very impressive, the bubble being +pulled inward or towards the axial line, sharply and suddenly, as if the +oxygen were highly magnetic.' + +He next labours to establish the true magnetic zero, a problem not so +easy as might at first sight be imagined. For the action of the magnet +upon any gas, while surrounded by air or any other gas, can only be +differential; and if the experiment were made in vacuo, the action of +the envelope, in this case necessarily of a certain thickness, would +trouble the result. While dealing with this subject, Faraday makes +some noteworthy observations regarding space. In reference to the +Torricellian vacuum, he says, 'Perhaps it is hardly necessary for me to +state that I find both iron and bismuth in such vacua perfectly obedient +to the magnet. From such experiments, and also from general observations +and knowledge, it seems manifest that the lines of magnetic force can +traverse pure space, just as gravitating force does, and as statical +electrical forces do, and therefore space has a magnetic relation of its +own, and one that we shall probably find hereafter to be of the utmost +importance in natural phenomena. But this character of space is not +of the same kind as that which, in relation to matter, we endeavour to +express by the terms magnetic and diamagnetic. To confuse these +together would be to confound space with matter, and to trouble all +the conceptions by which we endeavour to understand and work out a +progressively clearer view of the mode of action, and the laws of +natural forces. It would be as if in gravitation or electric forces, +one were to confound the particles acting on each other with the space +across which they are acting, and would, I think, shut the door to +advancement. Mere space cannot act as matter acts, even though the +utmost latitude be allowed to the hypothesis of an ether; and admitting +that hypothesis, it would be a large additional assumption to suppose +that the lines of magnetic force are vibrations carried on by it, whilst +as yet we have no proof that time is required for their propagation, or +in what respect they may, in general character, assimilate to or differ +from their respective lines of gravitating, luminiferous, or electric +forces.' + +Pure space he assumes to be the true magnetic zero, but he pushes his +inquiries to ascertain whether among material substances there may not +be some which resemble space. If you follow his experiments, you will +soon emerge into the light of his results. A torsion-beam was +suspended by a skein of cocoon silk; at one end of the beam was fixed +a cross-piece 1 1/2 inch long. Tubes of exceedingly thin glass, filled +with various gases, and hermetically sealed, were suspended in pairs +from the two ends of the cross-piece. The position of the rotating +torsion-head was such that the two tubes were at opposite sides of, +and equidistant from, the magnetic axis, that is to say from the line +joining the two closely approximated polar points of an electro-magnet. +His object was to compare the magnetic action of the gases in the +two tubes. When one tube was filled with oxygen, and the other with +nitrogen, on the supervention of the magnetic force, the oxygen was +pulled towards the axis, the nitrogen being pushed out. By turning +the torsion-head they could be restored to their primitive position of +equidistance, where it is evident the action of the glass envelopes was +annulled. The amount of torsion necessary to re-establish equidistance +expressed the magnetic difference of the substances compared. + +And then he compared oxygen with oxygen at different pressures. One of +his tubes contained the gas at the pressure of 30 inches of mercury, +another at a pressure of 15 inches of mercury, a third at a pressure +of 10 inches, while a fourth was exhausted as far as a good air-pump +renders exhaustion possible. 'When the first of these was compared with +the other three, the effect was most striking.' It was drawn towards +the axis when the magnet was excited, the tube containing the rarer gas +being apparently driven away, and the greater the difference between the +densities of the two gases, the greater was the energy of this action. + +And now observe his mode of reaching a material magnetic zero. When +a bubble of nitrogen was exposed in air in the magnetic field, on the +supervention of the power, the bubble retreated from the magnet. A less +acute observer would have set nitrogen down as diamagnetic; but Faraday +knew that retreat, in a medium composed in part of oxygen, might be due +to the attraction of the latter gas, instead of to the repulsion of the +gas immersed in it. But if nitrogen be really diamagnetic, then a bubble +or bulb filled with the dense gas will overcome one filled with the +rarer gas. From the cross-piece of his torsion-balance he suspended his +bulbs of nitrogen, at equal distances from the magnetic axis, and found +that the rarefaction, or the condensation of the gas in either of the +bulbs had not the slightest influence. When the magnetic force was +developed, the bulbs remained in their first position, even when one +was filled with nitrogen, and the other as far as possible exhausted. +Nitrogen, in fact, acted 'like space itself'; it was neither magnetic +nor diamagnetic. + +He cannot conveniently compare the paramagnetic force of oxygen with +iron, in consequence of the exceeding magnetic intensity of the latter +substance; but he does compare it with the sulphate of iron, and finds +that, bulk for bulk, oxygen is equally magnetic with a solution of this +substance in water 'containing seventeen times the weight of the oxygen +in crystallized proto-sulphate of iron, or 3.4 times its weight of +metallic iron in that state of combination.' By its capability to +deflect a fine glass fibre, he finds that the attraction of this bulb +of oxygen, containing only 0.117 of a grain of the gas, at an average +distance of more than an inch from the magnetic axis, is about equal to +the gravitating force of the same amount of oxygen as expressed by its +weight. + +These facts could not rest for an instant in the mind of Faraday without +receiving that expansion to which I have already referred. 'It is hardly +necessary,' he writes, 'for me to say here that this oxygen cannot exist +in the atmosphere exerting such a remarkable and high amount of magnetic +force, without having a most important influence on the disposition of +the magnetism of the earth, as a planet; especially if it be remembered +that its magnetic condition is greatly altered by variations of its +density and by variations of its temperature. I think I see here the +real cause of many of the variations of that force, which have been, and +are now so carefully watched on different parts of the surface of the +globe. The daily variation, and the annual variation, both seem likely +to come under it; also very many of the irregular continual variations, +which the photographic process of record renders so beautifully +manifest. If such expectations be confirmed, and the influence of the +atmosphere be found able to produce results like these, then we shall +probably find a new relation between the aurora borealis and the +magnetism of the earth, namely, a relation established, more or less, +through the air itself in connection with the space above it; and even +magnetic relations and variations, which are not as yet suspected, +may be suggested and rendered manifest and measurable, in the further +development of what I will venture to call Atmospheric Magnetism. I may +be over-sanguine in these expectations, but as yet I am sustained in +them by the apparent reality, simplicity, and sufficiency of the +cause assumed, as it at present appears to my mind. As soon as I +have submitted these views to a close consideration, and the test of +accordance with observation, and, where applicable, with experiments +also, I will do myself the honour to bring them before the Royal +Society.' + +Two elaborate memoirs are then devoted to the subject of Atmospheric +Magnetism; the first sent to the Royal Society on the 9th of October, +and the second on the 19th of November, 1850. In these memoirs he +discusses the effects of heat and cold upon the magnetism of the air, +and the action on the magnetic needle, which must result from thermal +changes. By the convergence and divergence of the lines of terrestrial +magnetic force, he shows how the distribution of magnetism, in +the earth's atmosphere, is effected. He applies his results to the +explanation of the Annual and of the Diurnal Variation: he also +considers irregular variations, including the action of magnetic storms. +He discusses, at length, the observations at St. Petersburg, Greenwich, +Hobarton, St. Helena, Toronto, and the Cape of Good Hope; believing +that the facts, revealed by his experiments, furnish the key to the +variations observed at all these places. + +In the year 1851, I had the honour of an interview with Humboldt, in +Berlin, and his parting words to me then were, 'Tell Faraday that I +entirely agree with him, and that he has, in my opinion, completely +explained the variation of the declination.' Eminent men have since +informed me that Humboldt was hasty in expressing this opinion. In +fact, Faraday's memoirs on atmospheric magnetism lost much of their +force--perhaps too much--through the important discovery of the relation +of the variation of the declination to the number of the solar spots. +But I agree with him and M. Edmond Becquerel, who worked independently +at this subject, in thinking, that a body so magnetic as oxygen, +swathing the earth, and subject to variations of temperature, diurnal +and annual, must affect the manifestations of terrestrial magnetism.[1] +The air that stands upon a single square foot of the earth's surface +is, according to Faraday, equivalent in magnetic force to 8160 lbs. +of crystallized protosulphate of iron. Such a substance cannot be +absolutely neutral as regards the deportment of the magnetic needle. But +Faraday's writings on this subject are so voluminous, and the theoretic +points are so novel and intricate, that I shall postpone the complete +analysis of these researches to a time when I can lay hold of them more +completely than my other duties allow me to do now. + + +Footnote to Chapter 12 + + [1] This persuasion has been greatly strengthened by the + recent perusal of a paper by Mr. Baxendell. + + + + +Chapter 13. + + Speculations: nature of matter: lines of force + +The scientific picture of Faraday would not be complete without a +reference to his speculative writings. On Friday, January 19, 1844, +he opened the weekly evening-meetings of the Royal Institution by a +discourse entitled 'A speculation touching Electric Conduction and the +nature of Matter.' In this discourse he not only attempts the overthrow +of Dalton's Theory of Atoms, but also the subversion of all ordinary +scientific ideas regarding the nature and relations of Matter and Force. +He objected to the use of the term atom:--'I have not yet found a +mind,' he says, 'that did habitually separate it from its accompanying +temptations; and there can be no doubt that the words definite +proportions, equivalent, primes, &c., which did and do fully express all +the facts of what is usually called the atomic theory in chemistry, were +dismissed because they were not expressive enough, and did not say all +that was in the mind of him who used the word atom in their stead.' + +A moment will be granted me to indicate my own view of Faraday's +position here. The word 'atom' was not used in the stead of definite +proportions, equivalents, or primes. These terms represented facts that +followed from, but were not equivalent to, the atomic theory. Facts +cannot satisfy the mind: and the law of definite combining proportions +being once established, the question 'why should combination take place +according to that law?' is inevitable. Dalton answered this question by +the enunciation of the Atomic Theory, the fundamental idea of which +is, in my opinion, perfectly secure. The objection of Faraday to Dalton +might be urged with the same substantial force against Newton: it might +be stated with regard to the planetary motions that the laws of +Kepler revealed the facts; that the introduction of the principle of +gravitation was an addition to the facts. But this is the essence of +all theory. The theory is the backward guess from fact to principle; +the conjecture, or divination regarding something, which lies behind +the facts, and from which they flow in necessary sequence. If Dalton's +theory, then, account for the definite proportions observed in the +combinations of chemistry, its justification rests upon the same basis +as that of the principle of gravitation. All that can in strictness be +said in either case is that the facts occur as if the principle existed. + +The manner in which Faraday himself habitually deals with his hypotheses +is revealed in this lecture. He incessantly employed them to gain +experimental ends, but he incessantly took them down, as an architect +removes the scaffolding when the edifice is complete. 'I cannot but +doubt,' he says, 'that he who as a mere philosopher has most power of +penetrating the secrets of nature, and guessing by hypothesis at her +mode of working, will also be most careful for his own safe progress +and that of others, to distinguish the knowledge which consists of +assumption, by which I mean theory and hypothesis, from that which is +the knowledge of facts and laws.' Faraday himself, in fact, was +always 'guessing by hypothesis,' and making theoretic divination the +stepping-stone to his experimental results. + +I have already more than once dwelt on the vividness with which he +realised molecular conditions; we have a fine example of this strength +and brightness of imagination in the present 'speculation.' He grapples +with the notion that matter is made up of particles, not in absolute +contact, but surrounded by interatomic space. 'Space,' he observes, +'must be taken as the only continuous part of a body so constituted. +Space will permeate all masses of matter in every direction like a net, +except that in place of meshes it will form cells, isolating each atom +from its neighbours, itself only being continuous.' + +Let us follow out this notion; consider, he argues, the case of a +non-conductor of electricity, such for example as shell-lac, with its +molecules, and intermolecular spaces running through the mass. In its +case space must be an insulator; for if it were a conductor it would +resemble 'a fine metallic web,' penetrating the lac in every direction. +But the fact is that it resembles the wax of black sealing-wax, which +surrounds and insulates the particles of conducting carbon, interspersed +throughout its mass. In the case of shell-lac, therefore, space is an +insulator. + +But now, take the case of a conducting metal. Here we have, as before, +the swathing of space round every atom. If space be an insulator there +can be no transmission of electricity from atom to atom. But there is +transmission; hence space is a conductor. Thus he endeavours to hamper +the atomic theory. 'The reasoning,' he says, 'ends in a subversion of +that theory altogether; for if space be an insulator it cannot exist +in conducting bodies, and if it be a conductor it cannot exist in +insulating bodies. Any ground of reasoning,' he adds, as if carried away +by the ardour of argument, 'which tends to such conclusions as these +must in itself be false.' + +He then tosses the atomic theory from horn to horn of his dilemmas. What +do we know, he asks, of the atom apart from its force? You imagine a +nucleus which may be called a, and surround it by forces which may +be called m; 'to my mind the a or nucleus vanishes, and the substance +consists in the powers of m. And indeed what notion can we form of the +nucleus independent of its powers? What thought remains on which to hang +the imagination of an a independent of the acknowledged forces?' Like +Boscovich, he abolishes the atom, and puts a 'centre of force' in its +place. + +With his usual courage and sincerity he pushes his view to its utmost +consequences. 'This view of the constitution of matter,' he continues, +'would seem to involve necessarily the conclusion that matter fills +all space, or at least all space to which gravitation extends; for +gravitation is a property of matter dependent on a certain force, and it +is this force which constitutes the matter. In that view matter is +not merely mutually penetrable;[1] but each atom extends, so to say, +throughout the whole of the solar system, yet always retaining its own +centre of force.' + +It is the operation of a mind filled with thoughts of this profound, +strange, and subtle character that we have to take into account in +dealing with Faraday's later researches. A similar cast of thought +pervades a letter addressed by Faraday to Mr. Richard Phillips, and +published in the 'Philosophical Magazine' for May, 1846. It is entitled +'Thoughts on Ray-vibrations,' and it contains one of the most singular +speculations that ever emanated from a scientific mind. It must be +remembered here, that though Faraday lived amid such speculations he did +not rate them highly, and that he was prepared at any moment to change +them or let them go. They spurred him on, but they did not hamper him. +His theoretic notions were fluent; and when minds less plastic than his +own attempted to render those fluxional images rigid, he rebelled. He +warns Phillips moreover, that from first to last, 'he merely threw out +as matter for speculation the vague impressions of his mind; for he gave +nothing as the result of sufficient consideration, or as the settled +conviction, or even probable conclusion at which he had arrived.' + +The gist of this communication is that gravitating force acts in lines +across space, and that the vibrations of light and radiant heat consist +in the tremors of these lines of force. 'This notion,' he says, 'as far +as it is admitted, will dispense with the ether, which, in another view +is supposed to be the medium in which these vibrations take place.' And +he adds further on, that his view 'endeavours to dismiss the ether but +not the vibrations.' The idea here set forth is the natural supplement +of his previous notion, that it is gravitating force which constitutes +matter, each atom extending, so to say, throughout the whole of the +solar system. + +The letter to Mr. Phillips winds up with this beautiful conclusion:-- + +'I think it likely that I have made many mistakes in the preceding +pages, for even to myself my ideas on this point appear only as the +shadow of a speculation, or as one of those impressions upon the mind +which are allowable for a time as guides to thought and research. He who +labours in experimental inquiries, knows how numerous these are, and how +often their apparent fitness and beauty vanish before the progress and +development of real natural truth.' + +Let it then be remembered that Faraday entertained notions regarding +matter and force altogether distinct from the views generally held by +scientific men. Force seemed to him an entity dwelling along the line in +which it is exerted. The lines along which gravity acts between the sun +and earth seem figured in his mind as so many elastic strings; indeed +he accepts the assumed instantaneity of gravity as the expression of the +enormous elasticity of the 'lines of weight.' Such views, fruitful in +the case of magnetism, barren, as yet, in the case of gravity, explain +his efforts to transform this latter force. When he goes into the open +air and permits his helices to fall, to his mind's eye they are +tearing through the lines of gravitating power, and hence his hope and +conviction that an effect would and ought to be produced. It must +ever be borne in mind that Faraday's difficulty in dealing with these +conceptions was at bottom the same as that of Newton; that he is in +fact trying to overleap this difficulty, and with it probably the limits +prescribed to the intellect itself. + +The idea of lines of magnetic force was suggested to Faraday by the +linear arrangement of iron filings when scattered over a magnet. He +speaks of and illustrates by sketches, the deflection, both convergent +and divergent, of the lines of force, when they pass respectively +through magnetic and diamagnetic bodies. These notions of concentration +and divergence are also based on the direct observation of his filings. +So long did he brood upon these lines; so habitually did he associate +them with his experiments on induced currents, that the association +became 'indissoluble,' and he could not think without them. 'I have been +so accustomed,' he writes, 'to employ them, and especially in my last +researches, that I may have unwittingly become prejudiced in their +favour, and ceased to be a clear-sighted judge. Still, I have always +endeavoured to make experiment the test and controller of theory +and opinion; but neither by that nor by close cross-examination in +principle, have I been made aware of any error involved in their use.' + +In his later researches on magne-crystallic action, the idea of lines of +force is extensively employed; it indeed led him to an experiment which +lies at the root of the whole question. In his subsequent researches on +Atmospheric Magnetism the idea receives still wider application, showing +itself to be wonderfully flexible and convenient. Indeed without this +conception the attempt to seize upon the magnetic actions, possible or +actual, of the atmosphere would be difficult in the extreme; but the +notion of lines of force, and of their divergence and convergence, +guides Faraday without perplexity through all the intricacies of the +question. After the completion of those researches, and in a paper +forwarded to the Royal Society on October 22, 1851, he devotes himself +to the formal development and illustration of his favourite idea. The +paper bears the title, 'On lines of magnetic force, their definite +character, and their distribution within a magnet and through space.' +A deep reflectiveness is the characteristic of this memoir. In his +experiments, which are perfectly beautiful and profoundly suggestive, he +takes but a secondary delight. His object is to illustrate the utility +of his conception of lines of force. 'The study of these lines,' he +says, 'has at different times been greatly influential in leading me to +various results which I think prove their utility as well as fertility.' + +Faraday for a long period used the lines of force merely as 'a +representative idea.' He seemed for a time averse to going further in +expression than the lines themselves, however much further he may +have gone in idea. That he believed them to exist at all times round a +magnet, and irrespective of the existence of magnetic matter, such as +iron filings, external to the magnet, is certain. No doubt the space +round every magnet presented itself to his imagination as traversed by +loops of magnetic power; but he was chary in speaking of the physical +substratum of those loops. Indeed it may be doubted whether the physical +theory of lines of force presented itself with any distinctness to his +own mind. The possible complicity of the luminiferous ether in magnetic +phenomena was certainly in his thoughts. 'How the magnetic force,' he +writes, 'is transferred through bodies or through space we know not; +whether the result is merely action at a distance, as in the case of +gravity; or by some intermediate agency, as in the case of light, heat, +the electric current, and (as I believe) static electric action. The +idea of magnetic fluids, as applied by some, or of Magnetic centres of +action, does not include that of the latter kind of transmission, but +the idea of lines of force does.' And he continues thus:--'I am more +inclined to the notion that in the transmission of the [magnetic] force +there is such an action [an intermediate agency] external to the magnet, +than that the effects are merely attraction and repulsion at a distance. +Such an affection may be a function of the ether; for it is not at all +unlikely that, if there be an ether, it should have other uses than +simply the conveyance of radiations.' When he speaks of the magnet in +certain cases, 'revolving amongst its own forces,' he appears to have +some conception of this kind in view. + +A great part of the investigation completed in October, 1851, was +taken up with the motions of wires round the poles of a magnet and the +converse. He carried an insulated wire along the axis of a bar magnet +from its pole to its equator, where it issued from the magnet, and was +bent up so as to connect its two ends. A complete circuit, no part of +which was in contact with the magnet, was thus obtained. He found that +when the magnet and the external wire were rotated together no current +was produced; whereas, when either of them was rotated and the other +left at rest currents were evolved. He then abandoned the axial wire, +and allowed the magnet itself to take its place; the result was the +same.[2] It was the relative motion of the magnet and the loop that was +effectual in producing a current. + +The lines of force have their roots in the magnet, and though they may +expand into infinite space, they eventually return to the magnet. Now +these lines may be intersected close to the magnet or at a distance from +it. Faraday finds distance to be perfectly immaterial so long as the +number of lines intersected is the same. For example, when the loop +connecting the equator and the pole of his barmagnet performs one +complete revolution round the magnet, it is manifest that all the lines +of force issuing from the magnet are once intersected. Now it matters +not whether the loop be ten feet or ten inches in length, it matters +not how it may be twisted and contorted, it matters not how near to the +magnet or how distant from it the loop may be, one revolution always +produces the same amount of current electricity, because in all +these cases all the lines of force issuing from the magnet are once +intersected and no more. + +From the external portion of the circuit he passes in idea to the +internal, and follows the lines of force into the body of the magnet +itself. His conclusion is that there exist lines of force within the +magnet of the same nature as those without. What is more, they are +exactly equal in amount to those without. They have a relation in +direction to those without; and in fact are continuations of them.... +'Every line of force, therefore, at whatever distance it may be taken +from the magnet, must be considered as a closed circuit, passing in some +part of its course through the magnet, and having an equal amount of +force in every part of its course.' + +All the results here described were obtained with moving metals. 'But,' +he continues with profound sagacity, 'mere motion would not generate a +relation, which had not a foundation in the existence of some previous +state; and therefore the quiescent metals must be in some relation to +the active centre of force,' that is to the magnet. He here touches the +core of the whole question, and when we can state the condition into +which the conducting wire is thrown before it is moved, we shall then +be in a position to understand the physical constitution of the electric +current generated by its motion. + +In this inquiry Faraday worked with steel magnets, the force of which +varies with the distance from the magnet. He then sought a uniform field +of magnetic force, and found it in space as affected by the magnetism +of the earth. His next memoir, sent to the Royal Society, December 31, +1851, is 'on the employment of the Induced Magnetoelectro Current as a +test and measure of magnetic forces.' He forms rectangles and rings, and +by ingenious and simple devices collects the opposed currents which are +developed in them by rotation across the terrestrial lines of magnetic +force. He varies the shapes of his rectangles while preserving their +areas constant, and finds that the constant area produces always the +same amount of current per revolution. The current depends solely on +the number of lines of force intersected, and when this number is kept +constant the current remains constant too. Thus the lines of magnetic +force are continually before his eyes, by their aid he colligates his +facts, and through the inspirations derived from them he vastly expands +the boundaries of our experimental knowledge. The beauty and exactitude +of the results of this investigation are extraordinary. I cannot +help thinking while I dwell upon them, that this discovery of +magneto-electricity is the greatest experimental result ever obtained by +an investigator. It is the Mont Blanc of Faraday's own achievements. +He always worked at great elevations, but a higher than this he never +subsequently attained. + + +Footnotes to Chapter 13 + + [1] He compares the interpenetration of two atoms to the + coalescence of two distinct waves, which though for a moment + blended to a single mass, preserve their individuality, and + afterwards separate. + + [2] In this form the experiment is identical with one made + twenty years earlier. See page 34. + + + + +Chapter 14. + + Unity and convertibility of natural forces: theory of the + electric current. + +The terms unity and convertibility, as applied to natural forces, are +often employed in these investigations, many profound and beautiful +thoughts respecting these subjects being expressed in Faraday's memoirs. +Modern inquiry has, however, much augmented our knowledge of the +relationship of natural forces, and it seems worth while to say a few +words here, tending to clear up certain misconceptions which appear to +exist among philosophic writers regarding this relationship. + +The whole stock of energy or working-power in the world consists of +attractions, repulsions, and motions. If the attractions and repulsions +are so circumstanced as to be able to produce motion, they are sources +of working-power, but not otherwise. Let us for the sake of simplicity +confine our attention to the case of attraction. The attraction exerted +between the earth and a body at a distance from the earth's surface is +a source of working-power; because the body can be moved by the +attraction, and in falling to the earth can perform work. When it rests +upon the earth's surface it is not a source of power or energy, because +it can fall no further. But though it has ceased to be a source of +energy, the attraction of gravity still acts as a force, which holds the +earth and weight together. + +The same remarks apply to attracting atoms and molecules. As long as +distance separates them, they can move across it in obedience to the +attraction, and the motion thus produced may, by proper appliances, +be caused to perform mechanical work. When, for example, two atoms of +hydrogen unite with one of oxygen, to form water the atoms are first +drawn towards each other--they move, they clash, and then by virtue of +their resiliency, they recoil and quiver. To this quivering motion +we give the name of heat. Now this quivering motion is merely the +redistribution of the motion produced by the chemical affinity; and this +is the only sense in which chemical affinity can be said to be converted +into heat. We must not imagine the chemical attraction destroyed, or +converted into anything else. For the atoms, when mutually clasped to +form a molecule of water, are held together by the very attraction which +first drew them towards each other. That which has really been expended +is the pull exerted through the space by which the distance between the +atoms has been diminished. + +If this be understood, it will be at once seen that gravity may in this +sense be said to be convertible into heat; that it is in reality no more +an outstanding and inconvertible agent, as it is sometimes stated to +be, than chemical affinity. By the exertion of a certain pull, through +a certain space, a body is caused to clash with a certain definite +velocity against the earth. Heat is thereby developed, and this is the +only sense in which gravity can be said to be converted into heat. In no +case is the force which produces the motion annihilated or changed into +anything else. The mutual attraction of the earth and weight exists when +they are in contact as when they were separate; but the ability of that +attraction to employ itself in the production of motion does not exist. + +The transformation, in this case, is easily followed by the mind's +eye. First, the weight as a whole is set in motion by the attraction +of gravity. This motion of the mass is arrested by collision with the +earth; being broken up into molecular tremors, to which we give the name +of heat. + +And when we reverse the process, and employ those tremors of heat to +raise a weight, as is done through the intermediation of an elastic +fluid in the steam-engine, a certain definite portion of the molecular +motion is destroyed in raising the weight. In this sense, and this +sense only, can the heat be said to be converted into gravity, or +more correctly, into potential energy of gravity. It is not that the +destruction of the heat has created any new attraction, but simply that +the old attraction has now a power conferred upon it, of exerting a +certain definite pull in the interval between the starting-point of the +falling weight and its collision with the earth. + +So also as regards magnetic attraction: when a sphere of iron placed +at some distance from a magnet rushes towards the magnet, and has its +motion stopped by collision, an effect mechanically the same as that +produced by the attraction of gravity occurs. The magnetic attraction +generates the motion of the mass, and the stoppage of that motion +produces heat. In this sense, and in this sense only, is there a +transformation of magnetic work into heat. And if by the mechanical +action of heat, brought to bear by means of a suitable machine, the +sphere be torn from the magnet and again placed at a distance, a power +of exerting a pull through that distance, and producing a new motion of +the sphere, is thereby conferred upon the magnet; in this sense, and in +this sense only, is the heat converted into magnetic potential energy. + +When, therefore, writers on the conservation of energy speak of tensions +being 'consumed' and 'generated,' they do not mean thereby that old +attractions have been annihilated and new ones brought into existence, +but that, in the one case, the power of the attraction to produce +motion has been diminished by the shortening of the distance between +the attracting bodies, and that in the other case the power of producing +motion has been augmented by the increase of the distance. These remarks +apply to all bodies, whether they be sensible masses or molecules. + +Of the inner quality that enables matter to attract matter we know +nothing; and the law of conservation makes no statement regarding that +quality. It takes the facts of attraction as they stand, and affirms +only the constancy of working-power. That power may exist in the form +of MOTION; or it may exist in the form of FORCE, with distance to act +through. The former is dynamic energy, the latter is potential +energy, the constancy of the sum of both being affirmed by the law of +conservation. The convertibility of natural forces consists solely +in transformations of dynamic into potential, and of potential into +dynamic, energy, which are incessantly going on. In no other sense has +the convertibility of force, at present, any scientific meaning. + +By the contraction of a muscle a man lifts a weight from the earth. But +the muscle can contract only through the oxidation of its own tissue or +of the blood passing through it. Molecular motion is thus converted into +mechanical motion. Supposing the muscle to contract without raising the +weight, oxidation would also occur, but the whole of the heat produced +by this oxidation would be liberated in the muscle itself. Not so when +it performs external work; to do that work a certain definite portion of +the heat of oxidation must be expended. It is so expended in pulling the +weight away from the earth. If the weight be permitted to fall, the heat +generated by its collision with the earth would exactly make up for that +lacking in the muscle during the lifting of the weight. In the case +here supposed, we have a conversion of molecular muscular action into +potential energy of gravity; and a conversion of that potential energy +into heat; the heat, however, appearing at a distance from its real +origin in the muscle. The whole process consists of a transference of +molecular motion from the muscle to the weight, and gravitating force is +the mere go-between, by means of which the transference is effected. + +These considerations will help to clear our way to the conception of +the transformations which occur when a wire is moved across the lines +of force in a magnetic field. In this case it is commonly said we have +a conversion of magnetism into electricity. But let us endeavour to +understand what really occurs. For the sake of simplicity, and with a +view to its translation into a different one subsequently, let us adopt +for a moment the provisional conception of a mixed fluid in the wire, +composed of positive and negative electricities in equal quantities, and +therefore perfectly neutralizing each other when the wire is still. By +the motion of the wire, say with the hand, towards the magnet, what the +Germans call a Scheidungs-Kraft--a separating force--is brought into +play. This force tears the mixed fluids asunder, and drives them in +two currents, the one positive and the other negative, in two opposite +directions through the wire. The presence of these currents evokes a +force of repulsion between the magnet and the wire; and to cause the one +to approach the other, this repulsion must be overcome. The overcoming +of this repulsion is, in fact, the work done in separating and impelling +the two electricities. When the wire is moved away from the magnet, a +Scheidungs-Kraft, or separating force, also comes into play; but now it +is an attraction that has to be surmounted. In surmounting it, currents +are developed in directions opposed to the former; positive takes the +place of negative, and negative the place of positive; the overcoming of +the attraction being the work done in separating and impelling the two +electricities. + +The mechanical action occurring here is different from that occurring +where a sphere of soft iron is withdrawn from a magnet, and again +attracted. In this case muscular force is expended during the act of +separation; but the attraction of the magnet effects the reunion. In the +case of the moving wire also we overcome a resistance in separating it +from the magnet, and thus far the action is mechanically the same as the +separation of the sphere of iron. But after the wire has ceased moving, +the attraction ceases; and so far from any action occurring similar to +that which draws the iron sphere back to the magnet, we have to overcome +a repulsion to bring them together. + +There is no potential energy conferred either by the removal or by +the approach of the wire, and the only power really transformed or +converted, in the experiment, is muscular power. Nothing that could in +strictness be called a conversion of magnetism into electricity occurs. +The muscular oxidation that moves the wire fails to produce within the +muscle its due amount of heat, a portion of that heat, equivalent to the +resistance overcome, appearing in the moving wire instead. + +Is this effect an attraction and a repulsion at a distance? If so, why +should both cease when the wire ceases to move? In fact, the deportment +of the wire resembles far more that of a body moving in a resisting +medium than anything else; the resistance ceasing when the motion is +suspended. Let us imagine the case of a liquid so mobile that the hand +may be passed through it to and fro, without encountering any sensible +resistance. It resembles the motion of a conductor in the unexcited +field of an electro-magnet. Now, let us suppose a body placed in +the liquid, or acting on it, which confers upon it the property of +viscosity; the hand would no longer move freely. During its motion, but +then only, resistance would be encountered and overcome. Here we have +rudely represented the case of the excited magnetic field, and the +result in both cases would be substantially the same. In both cases heat +would, in the end, be generated outside of the muscle, its amount being +exactly equivalent to the resistance overcome. + +Let us push the analogy a little further; suppose in the case of the +fluid rendered viscous, as assumed a moment ago, the viscosity not to be +so great as to prevent the formation of ripples when the hand is passed +through the liquid. Then the motion of the hand, before its final +conversion into heat, would exist for a time as wave-motion, which, on +subsiding, would generate its due equivalent of heat. This intermediate +stage, in the case of our moving wire, is represented by the period +during which the electric current is flowing through it; but that +current, like the ripples of our liquid, soon subsides, being, like +them, converted into heat. + +Do these words shadow forth anything like the reality? Such speculations +cannot be injurious if they are enunciated without dogmatism. I do +confess that ideas such as these here indicated exercise a strong +fascination on my mind. Is then the magnetic field really viscous, +and if so, what substance exists in it and the wire to produce the +viscosity? Let us first look at the proved effects, and afterwards turn +our thoughts back upon their cause. When the wire approaches the magnet, +an action is evoked within it, which travels through it with a velocity +comparable to that of light. One substance only in the universe has +been hitherto proved competent to transmit power at this velocity; +the luminiferous ether. Not only its rapidity of progression, but its +ability to produce the motion of light and heat, indicates that the +electric current is also motion.[1] Further, there is a striking +resemblance between the action of good and bad conductors as regards +electricity, and the action of diathermanous and adiathermanous bodies +as regards radiant heat. The good conductor is diathermanous to the +electric current; it allows free transmission without the development of +heat. The bad conductor is adiathermanous to the electric current, and +hence the passage of the latter is accompanied by the development of +heat. I am strongly inclined to hold the electric current, pure and +simple, to be a motion of the ether alone; good conductors being so +constituted that the motion may be propagated through their ether +without sensible transfer to their atoms, while in the case of bad +conductors this transfer is effected, the transferred motion appearing +as heat.[2] + +I do not know whether Faraday would have subscribed to what is here +written; probably his habitual caution would have prevented him from +committing himself to anything so definite. But some such idea filled +his mind and coloured his language through all the later years of his +life. I dare not say that he has been always successful in the treatment +of these theoretic notions. In his speculations he mixes together light +and darkness in varying proportions, and carries us along with him +through strong alternations of both. It is impossible to say how a +certain amount of mathematical training would have affected his work. +We cannot say what its influence would have been upon that force of +inspiration that urged him on; whether it would have daunted him, and +prevented him from driving his adits into places where no theory pointed +to a lode. If so, then we may rejoice that this strong delver at the +mine of natural knowledge was left free to wield his mattock in his own +way. It must be admitted, that Faraday's purely speculative writings +often lack that precision which the mathematical habit of thought +confers. Still across them flash frequent gleams of prescient wisdom +which will excite admiration throughout all time; while the facts, +relations, principles, and laws which his experiments have established +are sure to form the body of grand theories yet to come. + + +Footnotes to Chapter 14 + + [1] Mr. Clerk Maxwell has recently published an exceedingly + important investigation connected with this question. Even + in the non-mathematical portions of the memoirs of Mr. + Maxwell, the admirable spirit of his philosophy is + sufficiently revealed. As regards the employment of + scientific imagery, I hardly know his equal in power of + conception and clearness of definition. + + [2] One important difference, of course, exists between the + effect of motion in the magnetic field, and motion in a + resisting medium. In the former case the heat is generated + in the moving conductor, in the latter it is in part + generated in the medium. + + + + +Chapter 15. + + Summary. + +When from an Alpine height the eye of the climber ranges over the +mountains, he finds that for the most part they resolve themselves into +distinct groups, each consisting of a dominant mass surrounded by peaks +of lesser elevation. The power which lifted the mightier eminences, in +nearly all cases lifted others to an almost equal height. And so it is +with the discoveries of Faraday. As a general rule, the dominant result +does not stand alone, but forms the culminating point of a vast and +varied mass of inquiry. In this way, round about his great discovery of +Magneto-electric Induction, other weighty labours group themselves. His +investigations on the Extra Current; on the Polar and other Condition of +Diamagnetic Bodies; on Lines of Magnetic Force, their definite character +and distribution; on the employment of the Induced Magneto-electric +Current as a measure and test of Magnetic Action; on the Revulsive +Phenomena of the magnetic field, are all, notwithstanding the diversity +of title, researches in the domain of Magneto-electric Induction. + +Faraday's second group of researches and discoveries embrace the +chemical phenomena of the current. The dominant result here is the great +law of definite Electro-chemical Decomposition, around which are massed +various researches on Electro-chemical Conduction and on Electrolysis +both with the Machine and with the Pile. To this group also belongs +his analysis of the Contact Theory, his inquiries as to the Source of +Voltaic Electricity, and his final development of the Chemical Theory of +the pile. + +His third great discovery is the Magnetization of Light, which I should +liken to the Weisshorn among mountains--high, beautiful, and alone. + +The dominant result of his fourth group of researches is the discovery +of Diamagnetism, announced in his memoir as the Magnetic Condition of +all Matter, round which are grouped his inquiries on the Magnetism +of Flame and Gases; on Magne-crystallic action, and on Atmospheric +Magnetism, in its relations to the annual and diurnal variation of the +needle, the full significance of which is still to be shown. + +These are Faraday's most massive discoveries, and upon them his fame +must mainly rest. But even without them, sufficient would remain to +secure for him a high and lasting scientific reputation. We should +still have his researches on the Liquefaction of Gases; on Frictional +Electricity; on the Electricity of the Gymnotus; on the source of +Power in the Hydro-electric machine, the last two investigations being +untouched in the foregoing memoir; on Electro-magnetic Rotations; on +Regelation; all his more purely Chemical Researches, including his +discovery of Benzol. Besides these he published a multitude of minor +papers, most of which, in some way or other, illustrate his genius. I +have made no allusion to his power and sweetness as a lecturer. Taking +him for all in all, I think it will be conceded that Michael Faraday +was the greatest experimental philosopher the world has ever seen; and +I will add the opinion, that the progress of future research will tend, +not to dim or to diminish, but to enhance and glorify the labours of +this mighty investigator. + + + + +Chapter 16. + + Illustrations of Character. + +Thus far I have confined myself to topics mainly interesting to the man +of science, endeavouring, however, to treat them in a manner unrepellent +to the general reader who might wish to obtain a notion of Faraday as +a worker. On others will fall the duty of presenting to the world +a picture of the man. But I know you will permit me to add to the +foregoing analysis a few personal reminiscences and remarks, tending to +connect Faraday with a wider world than that of science--namely, with +the general human heart. + +One word in reference to his married life, in addition to what has been +already said, may find a place here. As in the former case, Faraday +shall be his own spokesman. The following paragraph, though written in +the third person, is from his hand:--'On June 12, 1821, he married, an +event which more than any other contributed to his earthly happiness and +healthful state of mind. The union has continued for twenty-eight years +and has in no wise changed, except in the depth and strength of its +character.' + +Faraday's immediate forefathers lived in a little place called Clapham +Wood Hall, in Yorkshire. Here dwelt Robert Faraday and Elizabeth his +wife, who had ten children, one of them, James Faraday, born in 1761, +being father to the philosopher. A family tradition exists that the +Faradays came originally from Ireland. Faraday himself has more than +once expressed to me his belief that his blood was in part Celtic, but +how much of it was so, or when the infusion took place, he was unable to +say. He could imitate the Irish brogue, and his wonderful vivacity may +have been in part due to his extraction. But there were other qualities +which we should hardly think of deriving from Ireland. The most +prominent of these was his sense of order, which ran like a luminous +beam through all the transactions of his life. The most entangled and +complicated matters fell into harmony in his hands. His mode of +keeping accounts excited the admiration of the managing board of this +Institution. And his science was similarly ordered. In his Experimental +Researches, he numbered every paragraph, and welded their various parts +together by incessant reference. His private notes of the Experimental +Researches, which are happily preserved, are similarly numbered: their +last paragraph bears the figure 16,041. His working qualities, moreover, +showed the tenacity of the Teuton. His nature was impulsive, but there +was a force behind the impulse which did not permit it to retreat. If in +his warm moments he formed a resolution, in his cool ones he made that +resolution good. Thus his fire was that of a solid combustible, not that +of a gas, which blazes suddenly, and dies as suddenly away. + +And here I must claim your tolerance for the limits by which I am +confined. No materials for a life of Faraday are in my hands, and what +I have now to say has arisen almost wholly out of our close personal +relationship. + +Letters of his, covering a period of sixteen years, are before me, +each one of which contains some characteristic utterance;--strong, yet +delicate in counsel, joyful in encouragement, and warm in affection. +References which would be pleasant to such of them as still live are +made to Humboldt, Biot, Dumas, Chevreul, Magnus, and Arago. Accident +brought these names prominently forward; but many others would be +required to complete his list of continental friends. He prized the love +and sympathy of men--prized it almost more than the renown which his +science brought him. Nearly a dozen years ago it fell to my lot to +write a review of his 'Experimental Researches' for the 'Philosophical +Magazine.' After he had read it, he took me by the hand, and said, +'Tyndall, the sweetest reward of my work is the sympathy and good will +which it has caused to flow in upon me from all quarters of the world.' +Among his letters I find little sparks of kindness, precious to no one +but myself, but more precious to me than all. He would peep into the +laboratory when he thought me weary, and take me upstairs with him to +rest. And if I happened to be absent, he would leave a little note for +me, couched in this or some other similar form:--'Dear Tyndall,--I was +looking for you, because we were at tea--we have not yet done--will you +come up?' I frequently shared his early dinner; almost always, in fact, +while my lectures were going on. There was no trace of asceticism in his +nature. He preferred the meat and wine of life to its locusts and wild +honey. Never once during an intimacy of fifteen years did he mention +religion to me, save when I drew him on to the subject. He then spoke +to me without hesitation or reluctance; not with any apparent desire to +'improve the occasion,' but to give me such information as I sought. +He believed the human heart to be swayed by a power to which science +or logic opened no approach, and, right or wrong, this faith, held in +perfect tolerance of the faiths of others, strengthened and beautified +his life. + +From the letters just referred to, I will select three for publication +here. I choose the first, because it contains a passage revealing the +feelings with which Faraday regarded his vocation, and also because it +contains an allusion which will give pleasure to a friend. + + +'Royal Institution. [ this is crossed out by Faraday ] + +'Ventnor, Isle of Wight, June 28, 1854. + +'My Dear Tyndall,--You see by the top of this letter how much habit +prevails over me; I have just read yours from thence, and yet I think +myself there. However, I have left its science in very good keeping, and +I am glad to learn that you are at experiment once more. But how is the +health? Not well, I fear. I wish you would get yourself strong first +and work afterwards. As for the fruits, I am sure they will be good, for +though I sometimes despond as regards myself, I do not as regards you. +You are young, I am old.... But then our subjects are so glorious, +that to work at them rejoices and encourages the feeblest; delights and +enchants the strongest. + +'I have not yet seen anything from Magnus. Thoughts of him always +delight me. We shall look at his black sulphur together. I heard from +Schonbein the other day. He tells me that Liebig is full of ozone, i.e., +of allotropic oxygen. + +'Good-bye for the present. + +'Ever, my dear Tyndall, + +'Yours truly, + +'M. Faraday.' + + +The contemplation of Nature, and his own relation to her, produced in +Faraday a kind of spiritual exaltation which makes itself manifest here. +His religious feeling and his philosophy could not be kept apart; there +was an habitual overflow of the one into the other. + +Whether he or another was its exponent, he appeared to take equal +delight in science. A good experiment would make him almost dance with +delight. In November, 1850, he wrote to me thus:--'I hope some day to +take up the point respecting the magnetism of associated particles. +In the meantime I rejoice at every addition to the facts and reasoning +connected with the subject. When science is a republic, then it gains: +and though I am no republican in other matters, I am in that.' All his +letters illustrate this catholicity of feeling. Ten years ago, when +going down to Brighton, he carried with him a little paper I had just +completed, and afterwards wrote to me. His letter is a mere sample of +the sympathy which he always showed to me and my work. + + +'Brighton, December 9, 1857. + +'My Dear Tyndall,--I cannot resist the pleasure of saying how very much +I have enjoyed your paper. Every part has given me delight. It goes on +from point to point beautifully. You will find many pencil marks, for I +made them as I read. I let them stand, for though many of them receive +their answer as the story proceeds, yet they show how the wording +impresses a mind fresh to the subject, and perhaps here and there you +may like to alter it slightly, if you wish the full idea, i.e., not an +inaccurate one, to be suggested at first; and yet after all I believe +it is not your exposition, but the natural jumping to a conclusion that +affects or has affected my pencil. + +'We return on Friday, when I will return you the paper. + +'Ever truly yours, + +'M. Faraday.' + + +The third letter will come in its proper place towards the end. + +While once conversing with Faraday on science, in its relations to +commerce and litigation, he said to me, that at a certain period of his +career, he was forced definitely to ask himself, and finally to decide +whether he should make wealth or science the pursuit of his life. He +could not serve both masters, and he was therefore compelled to choose +between them. After the discovery of magneto-electricity his fame was +so noised abroad, that the commercial world would hardly have considered +any remuneration too high for the aid of abilities like his. Even before +he became so famous, he had done a little 'professional business.' This +was the phrase he applied to his purely commercial work. His friend, +Richard Phillips, for example, had induced him to undertake a number of +analyses, which produced, in the year 1830, an addition to his income +of more than a thousand pounds; and in 1831 a still greater addition. He +had only to will it to raise in 1832 his professional business income +to 5000L. a year. Indeed double this sum would be a wholly insufficient +estimate of what he might, with ease, have realised annually during the +last thirty years of his life. + +While restudying the Experimental Researches with reference to the +present memoir, the conversation with Faraday here alluded to came to +my recollection, and I sought to ascertain the period when the question, +'wealth or science,' had presented itself with such emphasis to his +mind. I fixed upon the year 1831 or 1832, for it seemed beyond the range +of human power to pursue science as he had done during the subsequent +years, and to pursue commercial work at the same time. To test this +conclusion I asked permission to see his accounts, and on my own +responsibility, I will state the result. In 1832, his professional +business income, instead of rising to 5000L., or more, fell from 1090L. +4s. to 155L. 9s. From this it fell with slight oscillations to 92L. in +1837, and to zero in 1838. Between 1839 and 1845, it never, except in +one instance, exceeded 22L.; being for the most part much under this. +The exceptional year referred to was that in which he and Sir Charles +Lyell were engaged by Government to write a report on the Haswell +Colliery explosion, and then his business income rose to 112L. From +the end of 1845 to the day of his death, Faraday's annual professional +business income was exactly zero. Taking the duration of his life into +account, this son of a blacksmith, and apprentice to a bookbinder, +had to decide between a fortune of 150,000L. on the one side, and his +undowered science on the other. He chose the latter, and died a poor +man. But his was the glory of holding aloft among the nations the +scientific name of England for a period of forty years. + +The outward and visible signs of fame were also of less account to him +than to most men. He had been loaded with scientific honours from all +parts of the world. Without, I imagine, a dissentient voice, he was +regarded as the prince of the physical investigators of the present age. +The highest scientific position in this country he had, however, never +filled. When the late excellent and lamented Lord Wrottesley resigned +the presidency of the Royal Society, a deputation from the council, +consisting of his Lordship, Mr. Grove, and Mr. Gassiot, waited upon +Faraday, to urge him to accept the president's chair. All that argument +or friendly persuasion could do was done to induce him to yield to the +wishes of the council, which was also the unanimous wish of scientific +men. A knowledge of the quickness of his own nature had induced in +Faraday the habit of requiring an interval of reflection, before he +decided upon any question of importance. In the present instance he +followed his usual habit, and begged for a little time. + +On the following morning, I went up to his room and said on entering +that I had come to him with some anxiety of mind. He demanded its cause, +and I responded:--'Lest you should have decided against the wishes of +the deputation that waited on you yesterday.' 'You would not urge me to +undertake this responsibility,' he said. 'I not only urge you,' was my +reply, 'but I consider it your bounden duty to accept it.' He spoke of +the labour that it would involve; urged that it was not in his nature to +take things easy; and that if he became president, he would surely have +to stir many new questions, and agitate for some changes. I said that in +such cases he would find himself supported by the youth and strength +of the Royal Society. This, however, did not seem to satisfy him. Mrs. +Faraday came into the room, and he appealed to her. Her decision was +adverse, and I deprecated her decision. 'Tyndall,' he said at length, 'I +must remain plain Michael Faraday to the last; and let me now tell you, +that if I accepted the honour which the Royal Society desires to confer +upon me, I would not answer for the integrity of my intellect for a +single year.' I urged him no more, and Lord Wrottesley had a most worthy +successor in Sir Benjamin Brodie. + +After the death of the Duke of Northumberland, our Board of Managers +wished to see Mr. Faraday finish his career as President of the +Institution, which he had entered on weekly wages more than half a +century before. But he would have nothing to do with the presidency. He +wished for rest, and the reverent affection of his friends was to him +infinitely more precious than all the honours of official life. + +The first requisite of the intellectual life of Faraday was the +independence of his mind; and though prompt to urge obedience where +obedience was due, with every right assertion of manhood he intensely +sympathized. Even rashness on the side of honour found from him ready +forgiveness, if not open applause. The wisdom of years, tempered by a +character of this kind, rendered his counsel peculiarly precious to +men sensitive like himself. I often sought that counsel, and, with +your permission, will illustrate its character by one or two typical +instances. + +In 1855, I was appointed examiner under the Council for Military +Education. At that time, as indeed now, I entertained strong convictions +as to the enormous utility of physical science to officers of artillery +and engineers, and whenever opportunity offered, I expressed this +conviction without reserve. I did not think the recognition, though +considerable, accorded to physical science in those examinations at +all proportionate to its importance; and this probably rendered me more +jealous than I otherwise should have been of its claims. + +In Trinity College, Dublin, a school had been organized with reference +to the Woolwich examinations, and a large number of exceedingly +well-instructed young gentlemen were sent over from Dublin, to compete +for appointments in the artillery and the engineers. The result of +one examination was particularly satisfactory to me; indeed the marks +obtained appeared so eloquent that I forbore saying a word about them. +My colleagues, however, followed the usual custom of sending in brief +reports with their returns of marks. After the results were published, +a leading article appeared in 'The Times,' in which the reports were +largely quoted, praise being bestowed on all the candidates, except the +excellent young fellows who had passed through my hands. + +A letter from Trinity College drew my attention to this article, +bitterly complaining that whereas the marks proved them to be the best +of all, the science candidates were wholly ignored. I tried to set +matters right by publishing, on my own responsibility, a letter in +'The Times.' The act, I knew, could not bear justification from the War +Office point of view; and I expected and risked the displeasure of my +superiors. The merited reprimand promptly came. 'Highly as the Secretary +of State for War might value the expression of Professor Tyndall's +opinion, he begged to say that an examiner, appointed by His Royal +Highness the Commander-in-Chief, had no right to appear in the public +papers as Professor Tyndall has done, without the sanction of the War +Office.' Nothing could be more just than this reproof, but I did not +like to rest under it. I wrote a reply, and previous to sending it took +it up to Faraday. We sat together before his fire, and he looked very +earnest as he rubbed his hands and pondered. The following conversation +then passed between us:-- + +F. You certainly have received a reprimand, Tyndall; but the matter is +over, and if you wish to accept the reproof, you will hear no more about +it. + +T. But I do not wish to accept it. + +F. Then you know what the consequence of sending that letter will be? + +T. I do. + +F. They will dismiss you. + +T. I know it. + +F. Then send the letter! + +The letter was firm, but respectful; it acknowledged the justice of the +censure, but expressed neither repentance nor regret. Faraday, in +his gracious way, slightly altered a sentence or two to make it more +respectful still. It was duly sent, and on the following day I entered +the Institution with the conviction that my dismissal was there before +me. Weeks, however, passed. At length the well-known envelope appeared, +and I broke the seal, not doubting the contents. They were very +different from what I expected. 'The Secretary of State for War has +received Professor Tyndall's letter, and deems the explanation therein +given perfectly satisfactory.' I have often wished for an opportunity of +publicly acknowledging this liberal treatment, proving, as it did, that +Lord Panmure could discern and make allowance for a good intention, +though it involved an offence against routine. For many years +subsequently it was my privilege to act under that excellent body, the +Council for Military Education. + +On another occasion of this kind, having encouraged me in a somewhat +hardy resolution I had formed, Faraday backed his encouragement by an +illustration drawn from his own life. The subject will interest you, and +it is so sure to be talked about in the world, that no avoidable harm +can rise from its introduction here. + +In the year 1835, Sir Robert Peel wished to offer Faraday a pension, but +that great statesman quitted office before he was able to realise his +wish. The Minister who founded these pensions intended them, I believe, +to be marks of honour which even proud men might accept without +compromise of independence. When, however, the intimation first +reached Faraday in an unofficial way, he wrote a letter announcing his +determination to decline the pension; and stating that he was quite +competent to earn his livelihood himself. That letter still exists, but +it was never sent, Faraday's repugnance having been overruled by +his friends. When Lord Melbourne came into office, he desired to see +Faraday; and probably in utter ignorance of the man--for unhappily for +them and us, Ministers of State in England are only too often ignorant +of great Englishmen--his Lordship said something that must have deeply +displeased his visitor. All the circumstances were once communicated to +me, but I have forgotten the details. The term 'humbug,' I think, was +incautiously employed by his Lordship, and other expressions were used +of a similar kind. Faraday quitted the Minister with his own resolves, +and that evening he left his card and a short and decisive note at the +residence of Lord Melbourne, stating that he had manifestly mistaken his +Lordship's intention of honouring science in his person, and declining +to have anything whatever to do with the proposed pension. The +good-humoured nobleman at first considered the matter a capital joke; +but he was afterwards led to look at it more seriously. An excellent +lady, who was a friend both to Faraday and the Minister, tried to +arrange matters between them; but she found Faraday very difficult to +move from the position he had assumed. After many fruitless efforts, she +at length begged of him to state what he would require of Lord Melbourne +to induce him to change his mind. He replied, 'I should require from his +Lordship what I have no right or reason to expect that he would grant--a +written apology for the words he permitted himself to use to me.' The +required apology came, frank and full, creditable, I thought, alike to +the Prime Minister and the philosopher. + +Considering the enormous strain imposed on Faraday's intellect, the +boy-like buoyancy even of his later years was astonishing. He was often +prostrate, but he had immense resiliency, which he brought into action +by getting away from London whenever his health failed. I have already +indicated the thoughts which filled his mind during the evening of his +life. He brooded on magnetic media and lines of force; and the great +object of the last investigation he ever undertook was the decision of +the question whether magnetic force requires time for its propagation. +How he proposed to attack this subject we may never know. But he has +left some beautiful apparatus behind; delicate wheels and pinions, +and associated mirrors, which were to have been employed in the +investigation. The mere conception of such an inquiry is an illustration +of his strength and hopefulness, and it is impossible to say to what +results it might have led him. But the work was too heavy for his tired +brain. It was long before he could bring himself to relinquish it and +during this struggle he often suffered from fatigue of mind. It was at +this period, and before he resigned himself to the repose which marked +the last two years of his life, that he wrote to me the following +letter--one of many priceless letters now before me--which reveals, more +than anything another pen could express, the state of his mind at the +time. I was sometimes censured in his presence for my doings in the +Alps, but his constant reply was, 'Let him alone, he knows how to take +care of himself.' In this letter, anxiety on this score reveals itself +for the first time. + + +'Hampton Court, August 1, 1864. + +'My Dear Tyndall,--I do not know whether my letter will catch you, but I +will risk it, though feeling very unfit to communicate with a man whose +life is as vivid and active as yours; but the receipt of your kind +letter makes me to know that, though I forget, I am not forgotten, and +though I am not able to remember at the end of a line what was said at +the beginning of it, the imperfect marks will convey to you some sense +of what I long to say. We had heard of your illness through Miss Moore, +and I was therefore very glad to learn that you are now quite well; +do not run too many risks or make your happiness depend too much upon +dangers, or the hunting of them. Sometimes the very thinking of you, and +what you may be about, wearies me with fears, and then the cogitations +pause and change, but without giving me rest. I know that much of this +depends upon my own worn-out nature, and I do not know why I write +it, save that when I write to you I cannot help thinking it, and the +thoughts stand in the way of other matter. + +* * * * * + +'See what a strange desultory epistle I am writing to you, and yet I +feel so weary that I long to leave my desk and go to the couch. + +'My dear wife and Jane desire their kindest remembrances: I hear them in +the next room:... I forget--but not you, my dear Tyndall, for I am + +'Ever yours, + +'M. Faraday.' + + +This weariness subsided when he relinquished his work, and I have a +cheerful letter from him, written in the autumn of 1865. But towards +the close of that year he had an attack of illness, from which he never +completely rallied. He continued to attend the Friday Evening Meetings, +but the advance of infirmity was apparent to us all. Complete rest +became finally essential to him, and he ceased to appear among us. There +was no pain in his decline to trouble the memory of those who loved him. +Slowly and peacefully he sank towards his final rest, and when it came, +his death was a falling asleep. In the fulness of his honours and of his +age he quitted us; the good fight fought, the work of duty--shall I not +say of glory?--done. The 'Jane' referred to in the foregoing letter is +Faraday's niece, Miss Jane Barnard, who with an affection raised almost +to religious devotion watched him and tended him to the end. + +I saw Mr. Faraday for the first time on my return from Marburg in 1850. +I came to the Royal Institution, and sent up my card, with a copy of the +paper which Knoblauch and myself had just completed. He came down and +conversed with me for half an hour. I could not fail to remark the +wonderful play of intellect and kindly feeling exhibited by his +countenance. When he was in good health the question of his age would +never occur to you. In the light and laughter of his eyes you never +thought of his grey hairs. He was then on the point of publishing one +of his papers on Magnecrystallic action, and he had time to refer in +a flattering Note to the memoir I placed in his hands. I returned to +Germany, worked there for nearly another year, and in June, 1851, came +back finally from Berlin to England. Then, for the first time, and on my +way to the meeting of the British Association, at Ipswich, I met a man +who has since made his mark upon the intellect of his time; who has long +been, and who by the strong law of natural affinity must continue to +be, a brother to me. We were both without definite outlook at the time, +needing proper work, and only anxious to have it to perform. The chairs +of Natural History and of Physics being advertised as vacant in the +University of Toronto, we applied for them, he for the one, I for the +other; but, possibly guided by a prophetic instinct, the University +authorities declined having anything to do with either of us. If I +remember aright, we were equally unlucky elsewhere. + +One of Faraday's earliest letters to me had reference to this Toronto +business, which he thought it unwise in me to neglect. But Toronto had +its own notions, and in 1853, at the instance of Dr. Bence Jones, and on +the recommendation of Faraday himself, a chair of Physics at the Royal +Institution was offered to me. I was tempted at the same time to go +elsewhere, but a strong attraction drew me to his side. Let me say +that it was mainly his and other friendships, precious to me beyond all +expression, that caused me to value my position here more highly than +any other that could be offered to me in this land. Nor is it for its +honour, though surely that is great, but for the strong personal ties +that bind me to it, that I now chiefly prize this place. You might not +credit me were I to tell you how lightly I value the honour of being +Faraday's successor compared with the honour of having been Faraday's +friend. His friendship was energy and inspiration; his 'mantle' is a +burden almost too heavy to be borne. + +Sometimes during the last year of his life, by the permission or +invitation of Mrs. Faraday, I went up to his rooms to see him. The deep +radiance, which in his time of strength flashed with such extraordinary +power from his countenance, had subsided to a calm and kindly light, by +which my latest memory of him is warmed and illuminated. I knelt one day +beside him on the carpet and placed my hand upon his knee; he stroked +it affectionately, smiled, and murmured, in a low soft voice, the last +words that I remember as having been spoken to me by Michael Faraday. + +It was my wish and aspiration to play the part of Schiller to this +Goethe: and he was at times so strong and joyful--his body so active, +and his intellect so clear--as to suggest to me the thought that +he, like Goethe, would see the younger man laid low. Destiny ruled +otherwise, and now he is but a memory to us all. Surely no memory could +be more beautiful. He was equally rich in mind and heart. The +fairest traits of a character sketched by Paul, found in him perfect +illustration. For he was 'blameless, vigilant, sober, of good behaviour, +apt to teach, not given to filthy lucre.' He had not a trace of worldly +ambition; he declared his duty to his Sovereign by going to the levee +once a year, but beyond this he never sought contact with the great. +The life of his spirit and of his intellect was so full, that the things +which men most strive after were absolutely indifferent to him. 'Give me +health and a day,' says the brave Emerson, 'and I will make the pomp of +emperors ridiculous.' In an eminent degree Faraday could say the same. +What to him was the splendour of a palace compared with a thunderstorm +upon Brighton Downs?--what among all the appliances of royalty to +compare with the setting sun? I refer to a thunderstorm and a sunset, +because these things excited a kind of ecstasy in his mind, and to +a mind open to such ecstasy the pomps and pleasures of the world are +usually of small account. Nature, not education, rendered Faraday strong +and refined. A favourite experiment of his own was representative of +himself. He loved to show that water in crystallizing excluded all +foreign ingredients, however intimately they might be mixed with it. Out +of acids, alkalis, or saline solutions, the crystal came sweet and pure. +By some such natural process in the formation of this man, beauty and +nobleness coalesced, to the exclusion of everything vulgar and low. He +did not learn his gentleness in the world, for he withdrew himself from +its culture; and still this land of England contained no truer gentleman +than he. Not half his greatness was incorporate in his science, for +science could not reveal the bravery and delicacy of his heart. + +But it is time that I should end these weak words, and lay my poor +garland on the grave of this + + Just and faithful knight of God. + + + + + +End of the Project Gutenberg EBook of Faraday As A Discoverer, by John Tyndall + +*** END OF THIS PROJECT GUTENBERG EBOOK FARADAY AS A DISCOVERER *** + +***** This file should be named 1225.txt or 1225.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/1/2/2/1225/ + +Produced by An Anonymous Volunteer + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. Special rules, +set forth in the General Terms of Use part of this license, apply to +copying and distributing Project Gutenberg-tm electronic works to +protect the PROJECT GUTENBERG-tm concept and trademark. Project +Gutenberg is a registered trademark, and may not be used if you +charge for the eBooks, unless you receive specific permission. If you +do not charge anything for copies of this eBook, complying with the +rules is very easy. You may use this eBook for nearly any purpose +such as creation of derivative works, reports, performances and +research. They may be modified and printed and given away--you may do +practically ANYTHING with public domain eBooks. Redistribution is +subject to the trademark license, especially commercial +redistribution. + + + +*** START: FULL LICENSE *** + +THE FULL PROJECT GUTENBERG LICENSE +PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK + +To protect the Project Gutenberg-tm mission of promoting the free +distribution of electronic works, by using or distributing this work +(or any other work associated in any way with the phrase "Project +Gutenberg"), you agree to comply with all the terms of the Full Project +Gutenberg-tm License (available with this file or online at +http://gutenberg.org/license). + + +Section 1. General Terms of Use and Redistributing Project Gutenberg-tm +electronic works + +1.A. By reading or using any part of this Project Gutenberg-tm +electronic work, you indicate that you have read, understand, agree to +and accept all the terms of this license and intellectual property +(trademark/copyright) agreement. If you do not agree to abide by all +the terms of this agreement, you must cease using and return or destroy +all copies of Project Gutenberg-tm electronic works in your possession. +If you paid a fee for obtaining a copy of or access to a Project +Gutenberg-tm electronic work and you do not agree to be bound by the +terms of this agreement, you may obtain a refund from the person or +entity to whom you paid the fee as set forth in paragraph 1.E.8. + +1.B. "Project Gutenberg" is a registered trademark. It may only be +used on or associated in any way with an electronic work by people who +agree to be bound by the terms of this agreement. There are a few +things that you can do with most Project Gutenberg-tm electronic works +even without complying with the full terms of this agreement. See +paragraph 1.C below. There are a lot of things you can do with Project +Gutenberg-tm electronic works if you follow the terms of this agreement +and help preserve free future access to Project Gutenberg-tm electronic +works. See paragraph 1.E below. + +1.C. The Project Gutenberg Literary Archive Foundation ("the Foundation" +or PGLAF), owns a compilation copyright in the collection of Project +Gutenberg-tm electronic works. Nearly all the individual works in the +collection are in the public domain in the United States. If an +individual work is in the public domain in the United States and you are +located in the United States, we do not claim a right to prevent you from +copying, distributing, performing, displaying or creating derivative +works based on the work as long as all references to Project Gutenberg +are removed. Of course, we hope that you will support the Project +Gutenberg-tm mission of promoting free access to electronic works by +freely sharing Project Gutenberg-tm works in compliance with the terms of +this agreement for keeping the Project Gutenberg-tm name associated with +the work. You can easily comply with the terms of this agreement by +keeping this work in the same format with its attached full Project +Gutenberg-tm License when you share it without charge with others. + +1.D. The copyright laws of the place where you are located also govern +what you can do with this work. Copyright laws in most countries are in +a constant state of change. If you are outside the United States, check +the laws of your country in addition to the terms of this agreement +before downloading, copying, displaying, performing, distributing or +creating derivative works based on this work or any other Project +Gutenberg-tm work. The Foundation makes no representations concerning +the copyright status of any work in any country outside the United +States. + +1.E. Unless you have removed all references to Project Gutenberg: + +1.E.1. The following sentence, with active links to, or other immediate +access to, the full Project Gutenberg-tm License must appear prominently +whenever any copy of a Project Gutenberg-tm work (any work on which the +phrase "Project Gutenberg" appears, or with which the phrase "Project +Gutenberg" is associated) is accessed, displayed, performed, viewed, +copied or distributed: + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + +1.E.2. If an individual Project Gutenberg-tm electronic work is derived +from the public domain (does not contain a notice indicating that it is +posted with permission of the copyright holder), the work can be copied +and distributed to anyone in the United States without paying any fees +or charges. If you are redistributing or providing access to a work +with the phrase "Project Gutenberg" associated with or appearing on the +work, you must comply either with the requirements of paragraphs 1.E.1 +through 1.E.7 or obtain permission for the use of the work and the +Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or +1.E.9. + +1.E.3. If an individual Project Gutenberg-tm electronic work is posted +with the permission of the copyright holder, your use and distribution +must comply with both paragraphs 1.E.1 through 1.E.7 and any additional +terms imposed by the copyright holder. Additional terms will be linked +to the Project Gutenberg-tm License for all works posted with the +permission of the copyright holder found at the beginning of this work. + +1.E.4. Do not unlink or detach or remove the full Project Gutenberg-tm +License terms from this work, or any files containing a part of this +work or any other work associated with Project Gutenberg-tm. + +1.E.5. Do not copy, display, perform, distribute or redistribute this +electronic work, or any part of this electronic work, without +prominently displaying the sentence set forth in paragraph 1.E.1 with +active links or immediate access to the full terms of the Project +Gutenberg-tm License. + +1.E.6. You may convert to and distribute this work in any binary, +compressed, marked up, nonproprietary or proprietary form, including any +word processing or hypertext form. However, if you provide access to or +distribute copies of a Project Gutenberg-tm work in a format other than +"Plain Vanilla ASCII" or other format used in the official version +posted on the official Project Gutenberg-tm web site (www.gutenberg.org), +you must, at no additional cost, fee or expense to the user, provide a +copy, a means of exporting a copy, or a means of obtaining a copy upon +request, of the work in its original "Plain Vanilla ASCII" or other +form. Any alternate format must include the full Project Gutenberg-tm +License as specified in paragraph 1.E.1. + +1.E.7. Do not charge a fee for access to, viewing, displaying, +performing, copying or distributing any Project Gutenberg-tm works +unless you comply with paragraph 1.E.8 or 1.E.9. + +1.E.8. You may charge a reasonable fee for copies of or providing +access to or distributing Project Gutenberg-tm electronic works provided +that + +- You pay a royalty fee of 20% of the gross profits you derive from + the use of Project Gutenberg-tm works calculated using the method + you already use to calculate your applicable taxes. The fee is + owed to the owner of the Project Gutenberg-tm trademark, but he + has agreed to donate royalties under this paragraph to the + Project Gutenberg Literary Archive Foundation. Royalty payments + must be paid within 60 days following each date on which you + prepare (or are legally required to prepare) your periodic tax + returns. Royalty payments should be clearly marked as such and + sent to the Project Gutenberg Literary Archive Foundation at the + address specified in Section 4, "Information about donations to + the Project Gutenberg Literary Archive Foundation." + +- You provide a full refund of any money paid by a user who notifies + you in writing (or by e-mail) within 30 days of receipt that s/he + does not agree to the terms of the full Project Gutenberg-tm + License. You must require such a user to return or + destroy all copies of the works possessed in a physical medium + and discontinue all use of and all access to other copies of + Project Gutenberg-tm works. + +- You provide, in accordance with paragraph 1.F.3, a full refund of any + money paid for a work or a replacement copy, if a defect in the + electronic work is discovered and reported to you within 90 days + of receipt of the work. + +- You comply with all other terms of this agreement for free + distribution of Project Gutenberg-tm works. + +1.E.9. If you wish to charge a fee or distribute a Project Gutenberg-tm +electronic work or group of works on different terms than are set +forth in this agreement, you must obtain permission in writing from +both the Project Gutenberg Literary Archive Foundation and Michael +Hart, the owner of the Project Gutenberg-tm trademark. Contact the +Foundation as set forth in Section 3 below. + +1.F. + +1.F.1. Project Gutenberg volunteers and employees expend considerable +effort to identify, do copyright research on, transcribe and proofread +public domain works in creating the Project Gutenberg-tm +collection. Despite these efforts, Project Gutenberg-tm electronic +works, and the medium on which they may be stored, may contain +"Defects," such as, but not limited to, incomplete, inaccurate or +corrupt data, transcription errors, a copyright or other intellectual +property infringement, a defective or damaged disk or other medium, a +computer virus, or computer codes that damage or cannot be read by +your equipment. + +1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right +of Replacement or Refund" described in paragraph 1.F.3, the Project +Gutenberg Literary Archive Foundation, the owner of the Project +Gutenberg-tm trademark, and any other party distributing a Project +Gutenberg-tm electronic work under this agreement, disclaim all +liability to you for damages, costs and expenses, including legal +fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT +LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE +PROVIDED IN PARAGRAPH F3. YOU AGREE THAT THE FOUNDATION, THE +TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE +LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR +INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH +DAMAGE. + +1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a +defect in this electronic work within 90 days of receiving it, you can +receive a refund of the money (if any) you paid for it by sending a +written explanation to the person you received the work from. If you +received the work on a physical medium, you must return the medium with +your written explanation. The person or entity that provided you with +the defective work may elect to provide a replacement copy in lieu of a +refund. If you received the work electronically, the person or entity +providing it to you may choose to give you a second opportunity to +receive the work electronically in lieu of a refund. If the second copy +is also defective, you may demand a refund in writing without further +opportunities to fix the problem. + +1.F.4. Except for the limited right of replacement or refund set forth +in paragraph 1.F.3, this work is provided to you 'AS-IS' WITH NO OTHER +WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO +WARRANTIES OF MERCHANTIBILITY OR FITNESS FOR ANY PURPOSE. + +1.F.5. Some states do not allow disclaimers of certain implied +warranties or the exclusion or limitation of certain types of damages. +If any disclaimer or limitation set forth in this agreement violates the +law of the state applicable to this agreement, the agreement shall be +interpreted to make the maximum disclaimer or limitation permitted by +the applicable state law. The invalidity or unenforceability of any +provision of this agreement shall not void the remaining provisions. + +1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the +trademark owner, any agent or employee of the Foundation, anyone +providing copies of Project Gutenberg-tm electronic works in accordance +with this agreement, and any volunteers associated with the production, +promotion and distribution of Project Gutenberg-tm electronic works, +harmless from all liability, costs and expenses, including legal fees, +that arise directly or indirectly from any of the following which you do +or cause to occur: (a) distribution of this or any Project Gutenberg-tm +work, (b) alteration, modification, or additions or deletions to any +Project Gutenberg-tm work, and (c) any Defect you cause. + + +Section 2. Information about the Mission of Project Gutenberg-tm + +Project Gutenberg-tm is synonymous with the free distribution of +electronic works in formats readable by the widest variety of computers +including obsolete, old, middle-aged and new computers. It exists +because of the efforts of hundreds of volunteers and donations from +people in all walks of life. + +Volunteers and financial support to provide volunteers with the +assistance they need, is critical to reaching Project Gutenberg-tm's +goals and ensuring that the Project Gutenberg-tm collection will +remain freely available for generations to come. In 2001, the Project +Gutenberg Literary Archive Foundation was created to provide a secure +and permanent future for Project Gutenberg-tm and future generations. +To learn more about the Project Gutenberg Literary Archive Foundation +and how your efforts and donations can help, see Sections 3 and 4 +and the Foundation web page at http://www.pglaf.org. + + +Section 3. Information about the Project Gutenberg Literary Archive +Foundation + +The Project Gutenberg Literary Archive Foundation is a non profit +501(c)(3) educational corporation organized under the laws of the +state of Mississippi and granted tax exempt status by the Internal +Revenue Service. The Foundation's EIN or federal tax identification +number is 64-6221541. Its 501(c)(3) letter is posted at +http://pglaf.org/fundraising. Contributions to the Project Gutenberg +Literary Archive Foundation are tax deductible to the full extent +permitted by U.S. federal laws and your state's laws. + +The Foundation's principal office is located at 4557 Melan Dr. S. +Fairbanks, AK, 99712., but its volunteers and employees are scattered +throughout numerous locations. Its business office is located at +809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887, email +business@pglaf.org. Email contact links and up to date contact +information can be found at the Foundation's web site and official +page at http://pglaf.org + +For additional contact information: + Dr. Gregory B. Newby + Chief Executive and Director + gbnewby@pglaf.org + + +Section 4. Information about Donations to the Project Gutenberg +Literary Archive Foundation + +Project Gutenberg-tm depends upon and cannot survive without wide +spread public support and donations to carry out its mission of +increasing the number of public domain and licensed works that can be +freely distributed in machine readable form accessible by the widest +array of equipment including outdated equipment. Many small donations +($1 to $5,000) are particularly important to maintaining tax exempt +status with the IRS. + +The Foundation is committed to complying with the laws regulating +charities and charitable donations in all 50 states of the United +States. Compliance requirements are not uniform and it takes a +considerable effort, much paperwork and many fees to meet and keep up +with these requirements. We do not solicit donations in locations +where we have not received written confirmation of compliance. To +SEND DONATIONS or determine the status of compliance for any +particular state visit http://pglaf.org + +While we cannot and do not solicit contributions from states where we +have not met the solicitation requirements, we know of no prohibition +against accepting unsolicited donations from donors in such states who +approach us with offers to donate. + +International donations are gratefully accepted, but we cannot make +any statements concerning tax treatment of donations received from +outside the United States. U.S. laws alone swamp our small staff. + +Please check the Project Gutenberg Web pages for current donation +methods and addresses. Donations are accepted in a number of other +ways including checks, online payments and credit card donations. +To donate, please visit: http://pglaf.org/donate + + +Section 5. General Information About Project Gutenberg-tm electronic +works. + +Professor Michael S. Hart is the originator of the Project Gutenberg-tm +concept of a library of electronic works that could be freely shared +with anyone. For thirty years, he produced and distributed Project +Gutenberg-tm eBooks with only a loose network of volunteer support. + + +Project Gutenberg-tm eBooks are often created from several printed +editions, all of which are confirmed as Public Domain in the U.S. +unless a copyright notice is included. Thus, we do not necessarily +keep eBooks in compliance with any particular paper edition. + + +Most people start at our Web site which has the main PG search facility: + + http://www.gutenberg.org + +This Web site includes information about Project Gutenberg-tm, +including how to make donations to the Project Gutenberg Literary +Archive Foundation, how to help produce our new eBooks, and how to +subscribe to our email newsletter to hear about new eBooks. |